I came from Sportsbikes wanting a good all-rounder (and to slow down a bit) and bought a GS - 18 months and a lot of problems later I bought an S10 and could not be happier.
In the UK Yamaha's are expensive, so a GS is a fair bit cheaper, this has stopped the S10 selling very well, they tend to come up as ex demo's or pre-reg bikes at about £2k less than new price and then sell (why Yamaha don't jut cut the price £1500 and sell three times as many I just do not understand)
Anyway, this means few new bikes appear here, and used ones look to have lost a lot of money, but for the most part UK buyers have paid well under full price for one, I paid £9400 for mine with 149 miles on the clock, but on paper it looks like it lost £4k in the first year, in reality I have lost about £1500.
This makes them great value as a second owner in the UK, as a 1 year old S10 is about the same price as a 3 year old GS - do the maths on which will cost most in servicing and repairs.
People always chop and change bikes, in the UK many riders change every couple of years, often for the sake of change but mostly because the press tell them their bike is now crap and they need the latest and greatest bike as it is 0.15 seconds a lap quicker, or gets does the Quarter mile 1/10th quicker etc.
The people that love the S10 are those who are not bothered about following fashion, and understand what they are getting - a great all rounder, it is not the fastest, lightest, cheapest or best handling in the class, but it does everything very well and is probably the most reliable in its class, the latest BMW has a already got a large number of major issues - but is the darling of the press and the BMW marketing machine has managed to knock out as many in a year as Yamaha have in four :exclaim:
Bike sales success and desirability is often not related to how good or bad a bike is, but how it is perceived and marketed.
I think it sacrifices performance for reliability, weight for strength and price for quality - I cannot fault it, but I can find many other bikes that are better in several areas, but all of the others have a weakness or two I can happily live without, or more to the point refuse to live with.