For the most part, you're right. Enterprise hard drives tend to come with better agreements, especially for situations where data protection standards make it prohibitive to send a dead drive back to RMA it; often they'll just say to send back the controller board or the like. Oddly, however, one of the big design features for enterprise hard drives is that they'll give up faster if there's a mis-read, etc. Because you're striping your data over a large set of spindles, it's often faster to just throw your hands up and work from the parity disk until you can diagnose the issue. This is also why most good sized arrays will have hot-spares, so you can begin the rebuild while you figure out if the drive was just having a temporary glitch or not.