You can't make a big scale game with a year's worth of development time, especially under the current circumstances.
Yes, we saw Platinum, HG/SS and B/W release back-to-back for three years but this situation isn't comparable. Platinum was a minor update to a game that was made two years before that could be worked on with smaller team, while HG/SS was a remake that entailed most of the designing stage (and a lot of the foundation for the rest of the game) was already done for Game Freak. Because Platinum was the quickest kind of thing to make, I'd bet that HG/SS was in development at the same time as Platinum, before the two games came out.
But Black and White were a different story. Masuda remarked that they had been working on the game since 2006 and the release of Diamond and Pearl, which isn't surprising because they had to design a brand new region and Pokémon from scratch. Making a whole new game like Black & White is a tough job, and it's easy to see that they didn't have as much time as they would've liked to work on the game because it's full of unfinished content and other stuff that had to be put aside to hit the deadline.
Game Freak must have been working flat out until last August to get the game ready, so it's unrealistic to expect them to come out with another new game so soon after finishing their biggest project since Diamond and Pearl - remember how it took over a year to make Platinum and FRLG versions? (And don't forget that FR/LG wasn't nearly as good as HG/SS is, in terms of adding new content like new places, new music, new features and more storyline)
This is even more important if they want to release the game for the 3DS instead. Even if they did, it would just end up being a rushed product again, just like Black and White - and I'd rather wait one more year to get a better product for my money than have everything right now.