I think two drummers makes more sense than two bassists or two guitar. I mean fundamentally the drum set was a way to imitate multiple players, using pedals and such(really it's only an imitation). So, there are so many different ways to arrange the elements of the set, eg one emphasizing snare another emphasizing bass drum. This isn't the only way to do it, for example there is a wide variety of two person bass drum arrangements. Not to mention the tonal variation in cymbals that multiple drummers bring to the party. Furthermore, drums are often recorded on multi tracks, so even bands that only one drummer produce recordings that are essentially arranged for multiple drummers.
However, with bass there are just so many dynamics issues, and there is really only one octave between a bass and guitar so the bass is already a kind of double for guitar, but there is so little room between bass and guitar that it is difficult to put another instrument.
Having, two guitars again introduces so many more dynamics issues. I know bands do it all the time, but when you have trouble working the bass into the mix adding another guitar doesn't help. When it works(the best) the second guitarist usually has other functions like singing. I've played in a number of small guitar combos with several guitars, it's like hearing cats, getting them to comp for each other during solos, or getting there equpipment to jive.
I've also played percussion and drums with a number of other drummers, my mileage varries some get it others don't. I think the major rub is when a drummer who is committed to idea that he can play all the drum parts realizes that multiple drummers sound better, it's a harsh realization.