True, and a belt and an internal gear hub isn't something I'd choose for myself, unless I was looking to build up a bike that required no maintenance (a myth, I know), and woud be pretty much impervious to the elements. But I think that's the sort of use they have in mind.
I looks like it could be the same sort of belt used for automotive timing belts and such. If so, for use on a bike, it should last for a very long time, even accounting for exposure to sun and smog.
It's probably heavier than a chain and sprockets, but perhaps not that much heavier, though every gram counts.
The idea that you wouldn't have to worry about rain and grit is appealing.
Barry