Which game?
I can't say that's true of 1e, nor I think of 3e.
In my 1e variant, at any level except very high combats can easily go 10 rounds or more; 3 rounds would be considered very short, probably 5 to 8 is average. 15 is rare, 20 extremely rare. All-time record is 38 (!) rounds; a bizarre situation where one PC was fighting its own clone in melee - the PC was a Fighter with lots of hit points, crazy-ass AC, and not much going for it in the to-hit dept.; they needed something like a (19? 20?) to hit each other.