Ever consider reading the extended warranty agreement? Really, what if you moved to another state. Unless the dealer is actually the one who owns and sells the warranty service themselves it is highly unlikely you have to do the work there.
The ones we sold would warranty as long as proper maintenance was documented, whether done by shop or self. Of course if you show an oil change but the inside of the engine shows that isn't quite true (we had one with clean oil in the engine, but dirty oil in the filter) you may lose out.
Still, we did some warranty work that was possibly borderline just because of the number of warranties we sold versus the number of claims. The claims could have been disputed, but we didn't. We figured it was fair trade off. Besides we get paid to do the work.
KLX650C, Zephyr 550
SR500, Bultaco Sherpa T