Yeah - "normal" thing to do
They all do it. They claim they've selected certain drives and made them differently, in an "enterprise" ready state. Frankly I figure the extra bucks are twofold - one, to get enough dosh to cover the extra warranty claims from running the drives 24x7 for 5 years instead of 8x5 for 3 years (it's 44000 hours instead of 6280), and two, some extra margin for the resellers to make some money off the enterprise drives.
I really do doubt the quality is that different (of course having said that, I'll get home and I'll have lost 4 of the 20 disks in my array of consumer drives).
Sherlock would know whether or not the drives are different ...