There are differences in firmware though when you compare enterprise 7200rpm drives to desktop 7200rpm drives - error timeouts for example, and caching algorithms. You can tweak the drives to change the timeouts and recalibration times to make desktop drives behave better in arrays but they are _not_ otherwise identical. Also, although you can throw a SATA drive on a SAS controller (I have such a setup at home) throughput in an array is generally much better with SAS drives. At home I edit the timeouts on my personal drives, but I work in a data center and at work I would not take such a risk. If I screw up I risk down time for 300k people, and would put my job at risk. We buy enterprise drives across the board for servers.Throughput also isn't as critical on my home system. Running desktop drives on an array controller comes with certain risks, even if you know what you're doing. I have daily backups running at home to mitigate the risk.
Run desktop drives in an enterprise array, go ahead, and you'll see drives regularly drop out of the array even though nothing is wrong with the drives. They paused to recalibrate or error correction exceeded a timeout (so reliability in an array CAN and WILL suffer). You can yank the drive and reinsert it then it will run just fine for a while, then another one might drop out. Not acceptable for the enterprise, plus desktop hard drives are not rated/tested for 100% duty cycle while enterprise drives are. They are very similar but not identical. If you need a server (a tertiary DNS server or whatever) with a single drive, a desktop drive may be fine, but do NOT run a desktop drive in an array in the enterprise. Sooner or later you WILL regret it when 2-3 drives drop out of an array and you get called in at 2:00am to rebuild the server. Or, you could tweak the timeouts, risk fucking it up and put your job at risk.
And, on the higher end (such as you would install in an EMC or Netapp filer), have you seen any 10000 or 15000rpm desktop drives that compare to enterprise drives? I haven't.