I think it's worth pointing out a game mechanic which has a major impact on how sensible it is to roleplay your character stats: point buy.
If you're playing on a system where you roll for your stats, roleplaying those stats can actually be fun and interesting. I rolled a 6 for INT but an 18 for CHA. Whoops! Roleplaying that out could be a fun challenge.
But if you're using point buy, you already know what stats you're getting. Hey, your fighter is high on STR and low on INT. Shocking, I know!
Sarcasm aside, your point buy fighter is going to have the same stats as every other fighter built using the same system, with minor variations (maybe you have a little more CON and the other guy has a little more WIS, but it's probably only a couple points difference either way). If you require your players to closely roleplay their stats, basically every fighter will be roughly the same.
When you're rolling randomly for them, ability scores are an opportunity for roleplay. When you're using point buy, they're a straight jacket.
Since your stats are largely predetermined, you're not going to get to play that intelligent fighter. Fighters need INT as a dump stat. If you pump a lot of points into INT they get no mechanical return, which means it's a lot harder to do their job. Sure, you could gimp yourself in the name of roleplaying, but even if you're okay with that your party may not appreciate the fact that their fighter can't tank.
To be fair, both 3.5 and 4e provide class choices for the 'warrior who fights with brains instead of brawn' archetype. But if you want to go straight fighter, but be SMRT? Well, your stats aren't going to help you.
I think if you run a point-buy-based game you need to let stats be what they are intended to be, mechanical effects, and give your players the freedom to roleplay them or not, as they prefer. They can still be guidelines, 'suggested builds', if you will. But since you're not going to see as nearly as much variation in stats among 4e fighters as you did in 2e fighters, roleplaying ability scores strictly just isn't that exciting.