I'm currently at a Trek dealership, and they're hit-&-miss. We actually could file a warranty claim for the sort of problem under discussion, but to make a long story short, the opportunity cost (for those of you who took Economics) of filing the claim and waiting to see if it got OK'ed would be higher than just throwing in a replacement spoke, truing the wheel, and sending it back out. Warrantying the entire wheel sidelines the customer's bike, and doesn't fix the root of the problem (the wheel's not suitable for ongoing heavy-hauler duty).

I've been in this situation before... used to have a big strong customer who rode tons of mileage and collected scrap metal in his rear basket to make ends meet. After he went through the OP's problems with his stock wheel, and with another cheap replacement wheel, I diplomatically explained that he needed a serious rear wheel. We hand-built him a 36-spoke Rhyno Lite with DT spokes and a Deore LX hub, and that was the end of that problem.