It's their wedding, it's not about you.
Dude, of course it's not about me, but it's not going to be easy to let it roll off that easy, either - you ask someone if you can make a couple kegs of beer for the party, and they say "No, I'd rather spend way too much money so that someone I barely know can make a beer he doesn't care about?" The way I see it, it's like if my wife's uncle, who is an amateur woodworker but pretty damn good at it, offered to build us a baby bed and we said no, we'd rather buy it from Ikea.
Maybe you really like black press board furniture?
Just enjoy the wedding. Other have given good suggestions. If your beer was selected, you would be to busy to just enjoy the day.
Edit - judge the pros beer and see what you like don't like. Compare to what you would have made. Gives you some data and talking points if it ever comes up later. I still say enjoy the day.