Have you SEEN the number of foundation/moisturiser adverts aimed specifically at men now, with all the women in the advert too paying attention to the guy
It's not difficult to understand. If you are good looking already, with reasonable skin, then adding light skin matching foundation is gonna make you look even better.
I have noticed a BIG difference in when I do wear a small amount of foundation and when I don't. Looking in the mirror when I have foundation on you couldn't TELL I was wearing foundation, but it makes my skin look healthier and perfect.
Girls want guys who have nice skin, styled hair, toned bodies nowadays - but then again this is from MY experience. It's not hard to understand why some guys who have all these have better relationships and sex lives than people who don't.
Your son isn't weird, he's realistic and wants what ever man wants; he understands that in today's world, it matters what people think. Even if you don't like the fact that it matters what people think - because of the media, mainly - they do judge you. Like you said, he has no problem with women, but it's not homosexual to want to look better and grab people's attention. There's always someone we're trying to impress: everyone.