But still, what you say means that to use the weapon, one needs training. Ok, but that's the same as with every other martial weapon.
A normal X-bow is a simple weapon, maybe due to its ease-of-use. If the repeating version needs training, then it should go into the Martial category, not the Exotic. I see the Exotic category as those rare, culture-specific, odd looking weapons that require special training besides what would be needed with a normal version of the weapon.
Example: the Elven swords in the Races of the Wild. They have the same size as normal swords (short, long and great swords) but are used in a slightly different way, that allows the user to wield them with more dexterous stances (hence, being eligible for W.Finesse feats). I totally understand the idea of these weapons being 'Exotic' since they're in exclusive possession of the Elven population and the Masters of its fighting stance are all Elven, thus, you would have to meet them in order to work with the sword AND you'd have to re-learn how to use a sword properly, if you already knew how to use a standard sword.
I don't see this kind of justification in the Repeating X-bow.
Hope this clarifies the subject a bit more.