The best drives have five year warranties from the manufacturer.
There are only about three manufactures left standing, so every drive comes off the assembly line of one of those three major manufacturers. OEMs, including Apple, buy batches of drives with different model numbers and no manufacturer warranty at a reduced price. Since they are different model numbers, you cannot claim against the actual manufacturer for warranty coverage. (In the case of Apple, you make your claim to Apple, on Apple's terms.)
The great unanswered questions are, "Are these 'off-brand' or 'OEM' drives as good as the ones with five year warranty? Are inferior components or inferior designs used? Are costs reduced by throwing out the best features, like fluid bearings, quiet motors, and state-of-the-art error recovery?"
A long warranty is supposed to ensure a long-lasting product. YOU do not want to be the guy who has to collect on the warranty -- you want to be one of many who benefit from buying a long-lasting product. We know that staying with the main-line Brands gives you a five year warranty. It may be that these designs are still new enough that the warranty is still important.
Drives are certainly cheap enough now that I am not moved to buy off-brand to save a few bucks.