So let's play devil's advocat here:
Let put ourselves in the shoes of Leica. What could they have done better in their current situation with descreasing Leica sales numbers and increasing demand for digital cameras?
First, a new lens mount would have broken their neck financially. The development of the R8 costed over 35 Mio DM (ca. 17.5 MIO Euro). This was one of the reason of the unsecure future after the IPO. And this was one of the reason why there was no way back to the old, smaller bodydesign (lens mount stayed the same).
If they would design a new lens mount, they have to offer also AF. This makes it even more complicated and more expensive. As we have seen with Contax, it is not that easy for a newcomer in AF to get it the first time perfectly done. And today nobody compares it to the first models of Canon or Nikon, they compare it to the 6th generation AF Top-of-the-line bodies.
The old Leica lenses would have been obviously useless in that case too. The solution Contax tried with the AX (AF by shifting the backplate und using still MF-lenses) was not really accepted in the community. So also no alternative for Leica 10 years later.
Secondly, the investements of the Leica costumers are significantly higher in this lens mount (body AND lenses), than for Canon or Nikon costumers. So a change would have hurted them a lot more.
Thirdly Leica has the same problem as any manufacturer nowadays: They have to make a decision today about a totally unknown future development within the next 2 years. The busines nowadays is very different than 10 years agao, when only film cameras played a role. Since digital innovation is so fast (like in computer industry), you make basically a bet what will be the right features/size/MP etc in 2 years.
In the computer industry it is even easier, because you have always the same box and you exchange only the internal parts. You can not do this with cameras. And ühotographers will not buy every 2 years a new 3000 USD camera, just because the specs are 2 years later differently.
So it makes sense to have waited so long for this. And it makes sense (if the assumption of Leica is correct) to offer a 10MP back. If it is true, that after a certain pixel amount, the further increase will be less significant/viewable, then we might really come with 10MP in a range which will be sufficient.
There are other sources who are stating that the Canon 1ds would rival medium format. Although I do not believe this (but have never compared), it shows that there must be a kind of "common sense" number, which will be enough for 99% of the users. Check yourself: How many prints have you done in the past bigger than A3? Even Contax ND owners are happy with a fullsize 6MP camera.
If 10MP is enough to print excellent A3-size images, I doubt that many Leica users (or even Canon and Nikon complainers) will worry about a competitor's 20MP camera. This is not the game "mine is bigger than yours".
We are talking about spending significant money here and I am sure many people will look very closely whether it is worth it to spend even a dollar more on something they do not need and can not see in their own prints.
Again, if the assumptions are correct, then also the argumentation, that the life-cycle of digital cameras will slow down and the models will not be replaced every 12-24 months. In this case a 10MP camera can stay there for a long time. Canon will not bring out a 20MP camera, if there is a risk that they can not sell enough of them. And looking at the argumentation above, it looks like it.
Last but not least, another issue is the quality of the chip - not the amount of pixels. For ex&le the size, the reaction to colours, noise, dust problems etc. I am sure that we will se many improvements there, but this is separated from the number game.
Look at the new Fuji Velvia 100F. Everybody waited for it and now it seems that the first reviewers are disappointed and prefer the old one, which came out 15 or 20 years ago. This shows also that there is a limit sooner or later, where you can not improve something anymore significantly. And then everybody will hesitate to spend for it additional money.
Leica is not stupid. They want to survive. So they talked with the industry specialist like Kodak etc. and based of there insights, made their decision.
The SD card for ex&le might sound strange in the moment, but it is a fact that it is smaller and smaller means in this industry also more future. It is not the question what is standard now, it is the question what is the standard in 2 years from now. And the SD cards have a great chnace to be it. Using a CF card would have made the body also even thicker. If you had already a R8/R9 in your hands, you know that this would kill the sales even more.
But because of this argument, I do not understand why they did not choose USB 2 instead of firewire. In 2 years IMHO, you will have a hard time to find firewire on new computers. But USB 2 will be there 4x in each computer. My guess is that there is either a technical restriction or, as the IMACON guy said in the press conference, they have just more experience with it. IMHO not a good argument. Leica buyers want to keep that back probably for 5 years (gosh, 900 euro per year...). Would be a pitty if they could not connect it to their computer without an adapter.
Looking at all this, the announcement was the only right thing Leica could have done. Everybody knows now that they have only "hot air" in their hands, only some signed contracts and estimations. Read the Chat and you will see that they basically can not say anything specific about the DR Back.
But do not undersestimate the signal that they gave to many Leica users. Just because of this, the current costumers will not switch to another brand before they have not seen the first testshots with this back. Leica users have made a long decision making process before they purchased Leica products. And they will not chnage their minds just like that.
As I always say to my clients, "the last thing that dies in a human mind is the hope". So Leica costumers will hope - and wait. And this gives Leica 2 more years to breath.
Dirk