For a clutch going out, thats very easy to blame on the driver. As far as a bad tranny, thats bogus to point at the driver. Generally, there is no hard evidence that it was thrashed on unless there is rubber in the wheel wells and no tread left on the tires.
The tranny in my Subaru started making noises at 57k and was replaced with no questions at all. I had to remove the downpipe, midpipe, and reflash back to stock, so if one were to look hard enough, they could have voided my warrenty then and there.
The funny thing is, Ive always heard horror stories about Subaru denying warrenties, I switch to mazda, and it seems even worse!