Normally I'd interpret it like you have, but the license specifically says that only redistributions must keep the licensing in tact. I don't know if that was an intentional thing on their part or just a mis-wording that they didn't mean, but it definitely says that you have to keep the licensing in tact if you redistribute it.

I'm guessing that it was intentional. There are some people willing to go through the effort to remove the licensing from the source and compile. Who cares! The real issue (in terms of losing profits) is if one person is able to remove the licensing and redistribute that change.

A patch to remove a registration check is arguably a tool for copyright infringement no matter what the license says (the author is still the copyright holder after all). But I'm certainly not a lawyer.