yeah they assume every women has similar hip/waist proportions at least when making pants sizes! it's really an inconvenient number system. the "juniors" and "women" sizes are completely different as well. juniors go from 3, 5, 7, 9.. etc. while womens go in 4, 6, 8, 10, 12..... it's ridiculous!
in juniors i'm actually a 5, but a 4 in womens. and i'm 5'2 so i also have that "pants are too long" problem. anyway, i find mens slacks to be *extremely* comfortable and i can go by waist measurement! 27 or 28 fits me fine.
also, i think our system is implemented because it helps companies sneak smaller size clothing lines to make women feel better about their size and thus, buy from that particular line more often. "i'm a size 6 at abercrombie! other places say i'm an 8 or 10" or something to that effect. it's a self-validation marketing tool.
i think victoria's secret also does this with their bras because i'm a "B" cup there, where i'm normally an A. and they always follow you around with tape measures... it's weird :P