The proliferation of save-or-die effects and adventure-breaking effects like etherealness and scrying also makes high-level adventuring more difficult to pull off, and we've addressed those issues as well.
Awesome. That's one of the major problems with higher level adventures.
As for fireball not doing 1d6 per level... who knows. I'm sure they wouldn't mess with it unless there were some good reason.
Here's my thinking - the people who are writing 4e
love D&D, and they're going to do their best to make D&D awesome. They're not going to change fireball just because they can... they're changing it so it works better with the game, so the game itself works better.
I love what they said about needing to change the math behind the game, it's absolutely right. There's a ton of math going on in the background that previous editions barely even thought about. Guesswork, gut feelings, and yes, playtesting are what made the old editions playable. I'm really glad they're taking the guesswork and gut instinct out of the equation and really looking at the math behind the game. They're still going to playtest it. They're still going to get feedback from real people who play D&D and love it.
Just wait for the details to emerge, I think you'll be pleasantly surprised. Maybe you house rule fireball back to 1d6/level.... but maybe, just maybe, you listen to their reasoning, and decide that their way is better. After all, it's not like they're getting rid of fireball, so in-game, it should feel just about the same, wizard points, things go boom, and all is right with the world.
-Nate