While you can certainly add me to the list of those will will be disappointed with the additional $4.99 charge, I am not convinced they will grandfather all of us (despite their rhetoric to "the street" that there would be no additional charges). I hope I am wrong, but consider the following:
If you look at the Powerpoint, there are two categories of existing customers -- those "with legacy HD equipment" and those considered to be "remaining legacy customers". Only those with legacy HD equipment are grandfathered -- the remaining legacy customers are subject to the $4.99 charge for the HD-Extra Pack. Depending on how they define legacy HD equipment, it could be that those who have the MPEG-4 capable boxes wouldn't be grandfathered (i.e., the legacy equipment could be the non-MPEG-4 capable boxes). That would make logical sense since they will only get their current programming after the upgrade -- no gain or loss of channels.
Again, I hope I am wrong, but someone's gotta pay for all of those new satellites. Frankly, I've thought the $9.99 now was overpriced, but I also didn't think we'd end up getting "hundreds" of HD channels at our current monthly rates. On the other hand, Cablevision is advertising "no extra charge for HD" and has been slowly adding channels so this may be a competitive need for DirecTV.