I'm pretty sure compatibility isn't the reason of that choice.
An alternative explanation to a very confident Apple is just that they changed their attitude about all this, thinking there is not really much of a difference between them providing a countdown or others doing it (before the last Keynote this countdown webpage got pretty huge), between them providing a liveblog or others doing it (there are always many liveblogs with often crappy photos, so why not shot beautiful photos and provide them directly?), unaware that would hype up the event.
I don’t think it’s that, but if they are sufficiently tone-deaf that could be the case. Apple historically hasn’t really been, definitely not when it comes to their events, but who knows …
I still expect Apple to do something very, very big with TV.