I wouldn't be surprised if it was that or less. Considering most times the publisher has already fronted money for developement. It's possible maybe royalties would go up after the publisher has recouped it's initial investment, but the more likely situation is that the title goes into the bargain segment around that time.
There's also a possibility that the developer gets no royalties until the investment from the publisher has been recouped (IE - after a certain number of titles have sold).
After all, unless the developer (like ID/Epic for example) fund their own developement, then the publisher is taking on most of the risk.
Oh and I don't remember where I got the info from. This was years ago during the XBOX years where I came across it.
Regards,
SB