1) They were lazy.
2) They only received a single unit for their testing.
Take your pick. I think #2 is more likely.
Oh, wait -- you mean Velociraptors in Raid0, not X25M. They didn't bother because real-world performance is virtually unchanged (exception: server applications) with or without raid0. The biggest thing you get from raid0 is double the chance for total hdd failure. Remember, if either drive fails you lose the entire raid array (along with all your data, as it is spread across both drives).