It doesn't take 2 months to make a game
It usually takes longer, off the top of my head I'm pretty sure that Gen 5 came out not long ago (few months maybe). Unless they just rip out the gen 5 engine and remake the main series (gen 3 remake or whatever) just change the story line or whatever then yah it could be done quicker.. but then they have to undergo bug testing and all that.
Yeah I agree, main series games take time, they were probably starting planning for Black and White right after Gen 4, not to mention Game Freak spent about one and a half years developing the story and characters.
At least we're getting Pokemon games still to fill in the gap.