Three years is as good as it gets, in terms of duration of a home theater projector warranty. There are a very few projectors with a better warranty, however, although, not a longer one. For example, Epson offers three years on their Pro Cinema series (only two years on the less expensive Home Cinema projectors). Epson however, offers their replacement program for all three years. Even better, it offers a 24 hour timeline for them to ship out the replacement.
Optoma, if I remember correctly, offers pretty much the same warranty as Epson, on their HD81-LV flagship home theater projector, but not on their many less expensive projectors.
BenQ has a very good record of supporting their products. About three years ago, after launching their PE7700, one of the most popular home theater projectors at the time, the PE7700's started blowing lamps. I mean that lamps were dying between 300 and 700 hours for just about everyone. Once a bit of time passed, BenQ came through, first they started sending out free replacement lamps to those who had them fail. After they finally nailed the problem down, they upgraded every PE7700 out there, paying round trip freight, upgrading the firmware, and replacing the lamp. There were a few glitches, such as initially a shortage of lamps, but ultimately, BenQ came through in style. I was a dealer at the time, and we had sold several hundred of the PE7700's. We just pointed our customers to BenQ, and they all got taken proper care .
Bottom line: An extremely good warranty, from a company that has a good reputation for standing behind their products.