No idea, I just know that it is and there are more than a few games unfortunately that do lock. I don't think copying WipEout HD save-files to other systems work either. I tried that and the data is gone - although I didn't spend as much time as getting that one to work as I did with Soul Calibur 4.
The decision to do these things may be down to the developer, but ultimately, it should be Sony to set up rules about how certain things are done and guarantee a consistent experience throughout.
I see why some devs do it, although in most cases, I just think it's short sighted and ignores some of the issues. For instance: How can a legimate consumer copy his save file to new PS3? Even if this now works in some cases, what if he also decides to change his online PSN-id?
This is actually the reason why I haven't yet bought a slim for myself yet. Besides the missing B/C feature, I just don't want to go through the hassle of losing some of my game-saves.