Well, apart from obvious differences in the reproductive organs (since the chimps don't know that being naked is a social "faux pas", it's pretty easy to spot them), the females of the "great apes" have briasts!

Oh, yes they do. Covered in fur and smaller (they swell noticeably only while they're feeding cubs unlike those of humans which stay prominent for all the life) but still the all too familiar pear shape that we all know and love.
I'm pretty sure 99% people on Earth can distinguish a male chimpanzee from a female chimpanzee at first glance.
Hell most people can't even distinguish a male dog from a female one, unless they bow down and look.
If you still don't get my point, I'll say it more plainly.
You are asking about female falmers, and yet you(or most people) won't think about female saber tooth, mammoth, walrus, troll, etc. In this game however, all these creatures are gender unspecific.
You are asking it because falmers are humanoids but those are just beast. You see humanoids everyday and you think these falmers should just appear as what you see everyday. That's why you are bothered by it(lack of a female model).
You are not(or less) bothered by those beasts because you see them less often and to you a male and female aren't that different. However, if you ask a biologist who studies these kind of beasts everyday to play this game, it's very likely he/she will notice and be bothered by the lack of gender difference in these beasts as well.