I agree that this double standard exists and that it ought not to. On the other hand, I've observed some very masculine, unquestionably heterosexual men (some of them in my own family and circle of friends) commenting quite freely that they think other men are good-looking. I think people from all sorts of backgrounds vary widely in how seriously they take this unspoken 'code'.
Personally, when I hear a man refer to another man as 'handsome' or 'good-looking', I never think anything of it. I find that neither of them are especially loaded terms, and that (unless they are said in a very specific context) they don't carry implications that the speaker has any personal feelings of attraction.. the male equivalent of a word like 'pretty' or 'bonny', maybe. If a guy takes issue with the term, I'm inclined to question how secure he is in his masculinity.