They do more. And how wide is your saddle that you would be sitting on your lock? Whenever I don't have a bag with me, I always carry my u-lock in my belt. Its actually quite comfortable.
A Brooks b67. I have relatively wide sit bones and prefer a wider saddle for the same duties that most would use a medium width saddle (like a b17).
It seems to me that they're overpriced "designer" clothes that advertise more usefulness than what they actually provide. I can think of many places to carry a u-lock, and attached to a pair of pants isn't one of them.
To each their own though --