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I thought I had heard somewhere that pratically all threadless external headsets were the same design by cane creek, so presumed they might all share cartridge bearing design too...
Probably from me (well, a paraphrase), but it's the 99% which are made in Taiwan, not the 1% made in Yorkshire or Oregon. If you pull the bearings out and they say TH on them, they're made by TH Industries (owners of FSA) and probably common to millions of other headsets. If you measure the Hope ones and they're a common size with a TH bearing, you could replace them with a TH bearing, but realistically @edscoble is right, you won't pay much less for an FSA or Cane Creek branded cartridge, just because there's a minimum below which bike shops are simply not interested.
It's actually a pretty reasonable price for a cartridge bearing.