For Verlander, Houston is where he had the championships (one of them as a trade deadline acquisition), three All-Star nods and two Cys (plus a runner-up); with Detroit he had a ROTY, one CY (two runner-ups) and six All-Star nods. Also led the AL in WAR three times in Detroit. The difference between him and Schilling/Rolen is he obviously has nothing but fondness for his former team and vice-versa - so much so that he's now playing for them again.
The Halladay/Mussina solution (no cap at all) would make the most sense for him, but it's up to the player (or family). In Roy's case he was clearly so fond of the Philllies and they him that, arguably, his time there was over-weighed merely because of the perfect game and no-hitter, and fact that he got to pitch in the post-season at all. If memory serves the Phillies also changed the minimum years on their Wall of Fame requirements to accomodate him (as well as Moyer, who then mysteriously fell out of consideration).