I really don't like the questions about "best" practices for storage from MS. There is seldom enough information presented to properly answer those questions.

Sure, RAID10 offers better protection. RAID5 is cheaper. In discussions with EMC consultants as well as SQLIO sims you can get the same performance from both. If RAID5 is cheaper, you can add more disks and have more space in theory.

Case in point - at one client we had double the performance from RAID5 than the RAID10 (write and read were both better in SQLIO). Client could not afford to have RAID10 everywhere nor was there enough drive bays to compensate in favor of the RAID10.

If I had to use spinning disk then I would go RAID10 where possible. If I had the money I would use FusionIO not worry about the performance of the chosen array ;).