If you were to be offended by something like this, then the groom obviously made the right call to not ask you.
I'd be offended if he didn't invite me to his wedding, but short of that, what would it matter? In my situation, by Best Man has 2 brothers he may pick, or maybe one of the friends he actually hangs out with on a more regular basis (we live in different cities). Do you get pissed if you give someone a gift, but they don't get one for you?