DVDs are smaller and lighter than VHS tapes - I think that helps on the convenience front. Mobiles - the early ones had dreadful sound quality. We're into the later, "overtaking the legacy tech" stage with them.

But yeah, it's not a completely accurate theory. I think there is some truth in it, though. Your summary - "convenience is probably the most important driver for consumer take-up of new technologies, and retrograde steps in other aspects are sometimes insufficiently important to prevent this" - sounds right to me.

Cargoes - ta! Now, to find a Topman...