Clearly, neither cheaper nor lower priced.
They are, in fact 5400 RPM drives with 2 MB cache for a reason: who wants a 7200 RPM drive doing 33% more revolutions per day/week/year? That just shortens its lifespan and generates more heat. A 2 MB cache for streaming video is just as effective as an 8 MB cache.
In addition, these drives are tuned differently to be quieter (partially due to the slower spindle speed) and cooler. But they also have another key feature which is error recovery.
A desktop drive, when it encounters an error, hangs trying to re-read that data time and again. This is important when you want your Excel spreadsheet to work - every bit of data is important, so the drive must re-try until it ascertains that the data is bad. But do you care if one bit is wrong in your "ER" show? No - you won't even notice. But you will notice a stutter in a desktop drive because, rather than move ahead, it'll keep re-trying that data block. These QuickView drives will move ahead and get the next data and you'll never notice that one tiny blip.
Finally, how many people out there have found upgrade drives to cause problems when the boot drives were fine? We've seen several pretty old units where a drive causes a problem. A three-year-old Maxtor QuickView (or Quantum QuickView) drive is fine, but a newer Samsung desktop model is to blame.