Honestly, I find everyone quoting Sakurai as saying both versions will hold the same roster has little weight. True, he did, but he's said a lot of things and gone back on his word, such as his disinterest in 3rd party characters. Ya, so much for that one.. Him looking to limit clone characters was another major flip-flop.
He said this a long while back too, likely while Ice Climbers were still trying to be worked into the game (there has been proof of IC being coded as playable, but possibly abandoned). He very well may have said this in anticipation that IC could be programmed into the 3DS version.
So why wouldn't they announce this now? Because if this were true, 3DS sales would get cut in favor of the Wii U. Sure, many will by 3DS for mobility and ease, but a limited roster will dissuade many. The better strategy would be wait until after 3DS launch, preferably a week before the Wii U launch, THEN announce it, potentially reeling in double-purchases of smash. This also correlates with the linking rumors (assuming they imply the Wii U gets the extra characters, not the 3DS, also explaining why they are not coded in the 3DS.
I'm not saying the rumor is true, but we haven't proven it false yet. I think there's slim chance we're getting THAT many stages on Wii U, but again, you're talking about a same-game as the 3DS with much larger size capabilities, so it's possible..