If you look at earlier Pokémon, many of them have well rounded base stats, which is fine in-game, but makes them almost useless competitively. I think Game Freak has noticed/caused a shift toward competitive battling, and have adjusted base stats accordingly. I'm not sure that Pokémon are getting any stronger, just more biased towards one or two stats.
"I completed the National Dex at 12:03am on January 5th, 2013: if Gen VI is announced anytime soon I'm gonna be seriously angry."
January 8th, 2012: Pokémon X and Y announced. Seriously angry.