There are absolutely political reasons for it. Both the dividing founders reason you mentioned, plus the fact that single founders are more likely to be technical while when two people found one of them is likely to be a business founder. VCs feel they can control the business founder (or replace him if needed) much easier than the engineer, because VCs are not engineers. (and they are not entrepreneurs in my experience either, though they seem to think they are and are happy to trot out the "exits" they were vaguely involved in, usually via friends and family equity.)

I agree with your priority- a pair of fully dedicated good founders is ideal.