It can't be anything but noise.
Seagate and Samsung drivers exist largely to make Maxtor, IBM and WD drives look faster, I think.
Can't be price. Everyone else is cheaper (in small quantities, anyway). Go look at any page of price listings on pricewatch. Let me know how many times you had to click "Next" before you see a Seagate drive.
Can't be performance. Last time I remember a Seagate drive atop SR's ATA performance leaderboard, it was a Barracuda III, which was quickly dispatched (literally, after about three weeks) by the Maxtor DM40+.
Can't be reliability. I'll let Tannin comment on that one. Seagate manufactures ONE drive with a three year warranty. Doesn't speak highly of their products, does it?
Noise is the only thing Seagate brings to the table. Seagate should've been taken to task for their IDE products a LONG time ago.