Actually you are wrong (other then the fact that D10 could indeed do MPEG2 if they wanted it to).
The HR10 and any older receiver *cannot* tune to the new slots at 99 and 103. They don't know they exist. *THIS* the real reason why there is a receiver swapout, not MPEG4. But since DirecTV has to swap out everyone's receiver to see the new sat slots they decided to go to MPEG4 as well.
This is very similar to just like when they brought 119 online a few years ago. All the original receivers couldn't see the 119 sat. Thus I had to get all new receivers to get my locals off 119 since my old ones couldn't tune to the sat.
And you also state the 3 LNB dish will see D10. No, that's why you need the 5 LNB dish, to get the two new slots at 99 and 103 which is where D10 and D11 will go.
And one last thing, the Spaceways are doing MPEG4 only. Just HD locals and HD RSNs. Now there is no technical reason why they couldn't do MPEG2 an the Spaceways or on D10/D11 but there is no need to since you need a brand new receiver (H20 or HR20) to tune to these new sats anyway.
Not quite sure where you got your info but most of it is incorrect.
Bon,
You would think that this could be addressed with a software update, of course the dish would still have to be changed.
Jimbo