Reading that page, it appears that this due to US IP ownership agreements for employees. Is that correct?
If so, why isn't there an exception for personal-time-only contributions by single developers, or at least those outside a jurisdiction like the US where an employer may own each and all of your ideas and intellectual output? To be clear, I haven't lived or worked in the US, so this is all foreign and weird to me.
I'm pretty sure this is not true. In fact, it's the opposite of how it actually works. There's an explicit exception in the Copyright Act for a "work made for hire". If you're creating a opyrighted work for an employer, the employer is always the author of the work at the moment of inception.
There are separate state laws, iirc such as California, which makes parts of those kinds of provisions void.
In the past I've had contracts reprinted after pointing out errors in them.
So, yes, if it's a copy with my signature, it has the offending pieces crossed out.