It's true most of the time.
If they're really really hot, they're most likely str8.
I honestly hate it when people attribute it to "wanting what you can't have". It's not that at all. Str8 guys have a masculinity about them (which also seeps over into their appearance most of the time). It's also a confidence thing. Both of those affect the way a man looks, dresses, acts, etc. Of course I have seen my fair share of smoking hot gay men, but it's much more rare than seeing a group of smoking hot str8 men.
The idea of gay men being more attractive than str8 men may have been true a decade ago. But in this age where even str8 men can comfortably take care of themselves without being "accused" of being gay, str8s have taken back the crown imo.