StarCraft released: March 31, 1998
StarCraft 2 announced: May 19, 2007
Blizzard simply took their sweet ass time coming back to the Diablo and StarCraft franchises (ignoring the StarCraft: Ghost abomination).
Seriously, they can't milk WarCraft forever. Including Wrath of the Lich King that's five WarCraft games in a row. WarCraft 3, WarCraft 3: Frozen Throne, World of Warcraft, World of Warcraft: Burning Crusade, World of Warcraft: Wrath of the Lich King. That's about 6 years of WarCraft, the franchise is getting old.
Now it's not like I'm complaining about the first two, WC3 and WC3:FT were quite possibly the best single player RTS games I've played. WoW on the other hand is just a cash cow for Blizzard. I'd like a WC4 =/.
Then perhaps you're confused about what MMO means. Specifically the first M (hint). Yes you could play online (and offline), but that doesn't make it an MMO. Compare and contrast Counter-Strike with PlanetSide. There's also some differences between open and closed servers. So while Diablo 2 does share a few mechanics that typical MMOs have, it's definitely not one.
Depends what you want out of the game. I personally love RPGs for the story, so I'd say yes. But if you just want a clickfest RPG where you slaughter foes by the dozens then no =).
And for the record, Blizzard has always employed misdirection when they're about to announce something.
P.S. - EsKon, don't think I'm picking on you. Merely pointing out facts.