343 studios was partly bungie... They are people that worked on the games and storyline that were told by microsoft to keep the story as halo like as possible. Thanks to them other things happened like comics and halo legends for instance. Now that bungie won't make another halo game, they asked them to make it. So it's still in the hands of the original makers actually.
Not as as many as you think. According to Achronos over on the Bnet forums, you could count the number of people on one hand. The most Notable is Frank O'Connor as he is still the head of development (if I remember what the list said).
As for Halo 4, Master Chief's armor isn't as different when you get a good look at it.
File:Halo 4.JPG - Halo Nation - The Halo Franchise, Bungie, 343 Industries and more
Granted the aesthetics have changed drastically, it's still easily recognizable as the Mjolnir Mark VI armor
http://timenerdworld.files.wordpress.com/2010/05/halo-3.jpg?w=475
And in response to Shade88
Direct from the Halo 4 Wiki
"It is possible that the planet the
Dawn is approaching is Onyx - this theory is supported by the novel
Halo: Ghosts of Onyx - the portal may be opening
to release what is left of the
Spartan IIIs, and the rest of
Blue Team. This is, however, based on speculation and may not come to be."
Just as a little thought :rolleyes
As for the Cortana voice actor. My best guess is mostly what I've been reading. Either there is a new voice actor, or it was a temp for the trailer because the real voice actor was unavailable at the time.
EDIT: Oh and in response to the idea of the Nanobots altering the armor, I highly doubt it. If they could do all that then why couldn't they repair the giant scratch on the chest plate from when he crash landed after jumping off the Forerunner Dreadnaught in the opening of Halo 3?
Just a though.