Good point about the flushing, although my old stat and housing looked like the new one with no gunk in the cooling system at all.
I suppose with regular servicing/replacement of the coolant at the right intervals, and also using the advanced coolants, perhaps the cooling componants are getting blocked up far less than in the past. I have read others that replaced their stat and it also looked like new.
But from my research, the stat does tend to become lazy with age.
Perhaps not to the extent of putting on weight round its middle
.
Matt