I cleaned my dog yard this morning and will give a 10 yr warranty on their excrement. If you're unhappy at any time, I'll give you fresh excrement no questions asked!!
That said, Detroit Axle is probably getting the same parts as all other low end bearings, so they're probably "fine" for most applications for a few years.
Make no mistake: they've run the numbers and know that ~70% of Detroit Axle buyers have vehicles that are likely to die for other reasons in the next 2-3 years. A certain number will be totalled in accidents. Another 20% are likely to sell the vehicle in the next two years (including flippers). Of the ones that do experience a failure of their part, only 7% are likely to pursue warranty replacement via mail order.
My numbers are obviously pulled from my dog's posterior, but the point is that there's minimal financial risk in providing a "long" -- or even lifetime -- warranty