When I got my first D7 in 2007 I was expecting 'sealed' bearings too. Imagine my suprise, etc. The seals keep out some grime, the one on the rear hub fits o'er the axle onto the hub body. Thus, it 'sticks' to the axle and rotates agains the hub, adding friction, although not much. This is 'interesting.'

I've not had a problem with the hubs, they're freewheeling, and they have the advantage that they can be lubed in minutes. But the word 'sealed' is a bit like the 'water resistant' stamped on the back of my Casio watch. The rims are much better on the 2008/2009 bikes, the 2006/2007 joints on some of them were rough. The 2009 rims are stamped with the Dahon logo but could be made anywhere. I suspect Alex rims or some such.

The bottom brackets, cuppy and coney too, are quite smooth. I have a Shimano cartridge replacement for mine which I haven't bothered fitting until the original wears out, sometime in 2050. None of the rotating bits are overgreased from the factory, hence the attention to them, given that grease is almost as much a seal on these hubs as a lubricant. Hanging from the rafters in the garage is Mother's Raleigh shopper, bought new in 1951. Cup n' cones are fine after nearly fifty years of use in the English weather. It's had a few new tyres though.

So, back to the original post, in-exhaustive testing by one person has yet to break a Speed/Vitesse D7 hub. :-) One of the guys in Europe did 7000 miles through the UK, France and Spain on a Vitesse a couple of years ago, the only replacement parts were tyres and bar grips. That's fine for me, and the reason I bought my second D7.