Interesting, thanks!
Speaking of Avis, I also reserved with them yesterday for another trip and their reservation doesn't have a similar provision.
So how would Budget work it? Send you a bill to your e-mail address and hope you pay it?
(A "no show" charge would be in the nature of liquidated damages, seems to me, but since there's no actual obligation on the rental car company to have the car you "reserved" available, I wonder how they would get away with this.)