Yeah... You don't run RAID0 in a production environment unless one of these case are met, and even then you very much should question that decision. RAID0 exponentially increases your chances of a filesystem failure as you add each drive (e.g. 4 drives = 4 times likely to suffer data loss than a single drive).
The cases I would see as acceptable..
1. Scratch space. Meaning temporary disk storage space. Only there for doing things like resizing mpegs or whatnot. No data loss if it fails, and application should be smart enough to know it failed and not try to utilize it.
2. Very specific hardware load balanced setups, where individual machine failures are normal and expected.
4 drive RAID0 *will* be faster than 4 drive RAID10, but not by very much. You still will get roughly "4 times" the performance of a single drive in either case, minus overhead. The speed difference is negligible, and the chance of outage is guaranteed with RAID0. RAID10 you can sustain two drive failures, if they happen to be the correct drives. The single advantage RAID0 will give you, is the size of your array. (RAID10 will eat half the space in "overhead" - RAID0 has none)
Your sales guy is right, listen to him
Anyone recommending RAID0 for a production server simply does not have any experience in the matter.
-Phil