While that seems logical. I wonder? Dish is still setting up New Accounts with non MPG4 compatible equipment (IE 625's 322's 512's). I find it hard to believe the switch over date would be that close with all these SD receivers still going out.
Dish has not hinted at an MPEG-4 conversion for western arc. They have only rumored 8PSK conversion which these receivers can handle.
Dish can provide the HD for PBS if they provide the big 4. The big 4 just will go down in quality to fit PBS in, but I doubt it will really affect many markets.
I think the real reason is that Dish wants to delay the WA conversion to 8PSK, or roll it out slower to save money, this may force them to accellerate plans. And really they would only have to do it in the markets that need the space.
On EA it might delay new markets from being rolled out since they will have to use space being freed up on 72 from DIRECTV for PBS HD instead of other things. Eventually when 77 gets its spot beam satellite they will have the capacity.
They just want the FCC to rule that it is impossible for them to provide PBS so they do not have to make the hard choices while waiting for the new satellites to launch.