All manufacturers have varying levels of quality and performance in all of their models of hard drives. A bulk, white label bare drive is NOT going to be as good or last as long as, say a caviar black or green. That's why they have a 1 year warrantee, vice a 3 or 5 year warrantee for a boxed version (or something like that). I have a pair of original 10,000 RPM WD Raptors (74GB) that are more than 10 years old and run like a champ! In fact I only removed them to make room for a single SSD, and I threw them in a box made with spare parts to play around with Linux and media server software.
You get what you pay for, no matter what the brand. WD and Seagate are both solid.