Re: Does it bother you...
I hate seeing a head that's wider than the cabinet. Not only does it look wrong, it's also likely to be less stable. The feet on the head are probably closer to the edges of the cab (if they even fit), and there's part of the head hanging out over the cabinet, more likely to get bumped into and knocked off.
There's a lot to be said for not playing with the head on top of the cabinet. Sure the aesthetics and convenience are nice, but there's the risk of damage, and also the vibration. It's probably not the best idea to subject hot tubes and solder joints to extended, repetitive mechanical oscillations.
But I still totally do it when I'm not at home.