I guess it's just a personal "pet peeve"...I've been backpacking since the late 1980s; I've done the 2-step process many times with my old TAR mats, and always hated the back-and-forth fussing with the valve and pressing down with my arms and legs. (I like the idea of opening the valve while lying down, using body weight to partially collapse the pad, closing the valve, and re-rolling -- I've never tried that one!)
Clearly most people aren't annoyed by this in the way I am, (except David, to a lesser extent) -- so if there isn't a perceived problem, then no one would be interested in its solution, and even if it were invented, no one would buy it!
BTW, I get Aaron's point about the deflation valve on Exped (it's essentially just a "hole" that lets air out, and the air has no reason to try to get back in) -- but I'm still not clear on why some kind of deflation-only valve couldn't be fitted to a TAR-type mat... THIS is why I went to law school instead of Med/Engineering!!! Contracts, conveyancing, etc: easy; science: hard. ;~)