I've got a few Euro Saturns and a Japanese Saturn too. Recently I bought a Euro backup memory cart and it works fine in my Euro Saturns. I haven't been able to try it in my Japanese Saturn because I haven't had the cart slot fixed yet. But that's another story.
Anyway, I recently won a Japanese cart on Ebay. After the auction was complete, the seller contacted me to say that the cart didn't work on his Euro saturn and that if I didn't have a Japanese Saturn he'd refund the money. Considering that I was of the belief that carts worked universally I took him up on the offer of a refund. A couple of weeks later I won another Japanese cart. When it arrived I tried it in my Euro Saturns.
They didn't recognize it.
This is what confuses me: Have I just had a run of bad luck and come across two dead carts in rapid succession or is there more to it?
I only wonder if there is some sort of territory lock because of this:
Originally posted by Ram Cart manual
This product is intended for use in Japan only. SEGA will not be held responsible if this product is used outside Japa. Further, SEGA offers no warranty, service or support overseas. Sega does not authorize the export, use for profit, rental or leaseing of this product.
If the Action Replay Header and additional "Produced by or under license from..." screen are any indication, a region lockout system for carts does exist. Whether or not such a thing would be used by an official memory cart is beyond my knowledge...
The Action Replay ROM header isn't in the format described in the cartridge manuals, instead it's an almost-to-spec IP header. It's this fact that lead me to believe the cartridge fools the BIOS into thinking it's loading from the CD while it's actually copying code from the cart. (The header differs in some comment fields, like if the format was deduced by reverse-engineering, without access to manuals.)