are all beers ok with 3 to 4 week primary?

I understand the reason to leave brew in primary longer but are all brews ok to leave in primary that long?

I leave most beers in the primary for 3 weeks, but some beers are better drank fresh: hefeweizens and some pale ales/IPA's for instance. Many people will say though that 3 weeks is still fine for even those beers. I find hefeweizens get too dried out and clear if I leave them in the primary that long.

In the case of lagers, the length of the primary is tied to the progression of the fermentation, so each beer will be different.

I've never done that, but I don't see an issue with it if you like your results.

I normally leave my ales in the fermenter for 10-14 days or so, and another 5 days if I dryhop. I don't see any problems arising from leaving the beer in the fermenter for 4 weeks though. It's certainly not necessary, but it probably doesn't have much of a flavor impact.

I have always done 4 weeks primary, 4 weeks bottle. That's just how I roll.

From what I understand, really big beers (1.080+) could take longer than that. However, a standard gravity (1.050-ish) ale will only need a couple of weeks as Yooper indicated. So, in general:

Is it OK? - Yes
Is it necessary? - Probably not