You got something in writing saying the way you rode this bike was warrantied (especially the jumping part)?
Can't say I've seen xc bikes come with that kind of blessing in the warranty.
Then there's the whole reasonable lifetime of the product concept from the manufacturer's viewpoint (and the legal opinions that go along with that) and the consumer's understanding of "lifetime"...google lifetime warranty definition or reasonable lifetime warranty for some ideas. What's REI's specific warranty say in any case? You do have a written warranty to work off of, yes?
What's the point of mentioning the bikes are made in Taiwan? Where the majority of good bikes are coming from...
In any case I'd think that 10 years of heavy use of a bicycle is quite reasonable, but if you think you got a warranty that meant for your lifetime, that's not necessarily unusual either.