Out of an entire page of comments, you are the only one to get it right.
The legalese here has to do with code from ibooks being exported into the file, so that even if they have fixes for css bugs, etc, in the future, the formatting preferences can be preserved.
RE: Bison. Even after bison's licensing, some software companies are nervous about it - not that bison community is going to come after them - but that they might not completely own the binaries they produce. It's a really tough legal conundrum (code generated from a recipe), but luckily virtually everybody seems to be on the same page, insofar as useful tools like these should be used judiciously and without restriction.
In theory, Apple is being defensive, which is a little sad, but it is understandable Nominally, they pick the wrong side of this issue in order to protect their CSS.
Additionally, though, they create a headache for their users, which is something of a mortal sin in my book, and require many hours of additional labor to prepare books for other vending platforms. I very much wish that Apple would get off of their anti-competitive high horse and focus on building good tools without noxious restrictions. They have come pretty far by being very agressive about building a software silo. But at this point Apple needs to begin to transition to a softer sell on its platforms, or it will become another Bad Era Microsoft.