Come to think of it though, isn't it against the license of FPC for Scooter Software to use a modified FPC in production code without making the source available?
No. They don't distribute FPC itself. They only distribute its product.
GPL requires the sources availability only if the GPL-ed software is distributed.
(Note, that currently its taking its own toll on their development. As they've to (manually) keep up with FPC updates. It would be so much easier, if FPC was using git. So much easier to use and NOT to share. Must switch to git, asap!)