"How many reasonably geared (entry 80 raiding) people does it take for TBC 25man raids?"
That depends. Mount Hyjal and Black Temple were being cleared with 15 to 20 fully Sunwell geared players right before Wrath came out. I did a number of these raids myself. They were more difficult, sure, but when you had 15 or 20 players that had done the fights hundreds of times for a year, well, it's really second nature to many folks.
Sunwell was a different animal due to some of the DPS / Tanking / Healing checks throughout the instance. You'd have been hard pressed to do Brutallus with anything less than 22 people – and even that would be pushing it for most top-of-the-top-end guilds (pre nerf).
If you are going in with people that truly have been there for a year or more, I would expect it could be 10-maned easily. If the players are really top notch, the kind of god like players that you kind of wonder if they're cheating they're so good, you could probably see a 5-man clear MH/BT. For everyone else I'd recommend between 15 and 20 players.
Kara, Gruul, Mag, SSC, and most of TK can probably be 5-maned without too much hassle. I would say however that with Kael'thas you might run into significant problems. And remember too that several fights have legitimately hard mechanics which require extensive study and practice (ie: Kale'thas and Vashj). Even though the bosses might not hit hard, the actual encounters themselves still require coordination.
"While I understand it's called WoW Insider, I'm curious on what everyone at WoW Insider thinks about the upcoming Blizzard releases of StarCraft 2 and Diablo 3? Also, any plans for a StarCraft Insider and Diablo Insider?"
Everyone here is excited about both those titles, and we're gonna be first in line to get them. I personally had the chance to sit down and play them for several hours at BlizzCon thanks to the press room, and I can say that they're truly amazing games.
I don't think there are any plans for specific sites in the future, but I can't really say one way or another. We do already have excellent coverage of StarCraft II and Diablo 3 over at JoyStiq and Big Download. For some more coverage, check out the interview I did with Chris Sigaty (lead producer of StarCraft II) and some gameplay impressions of StarCraft II. Also take a look at Daniel Whitcomb's coverage of the Diablo 3 Class Panel and Diablo 3 Art and Lore Panel.