The ROMs are definitely still copyrighted. I don't know if the entity that owns the rights even knows they do (or perhaps there are multiple entities who think they have the rights, but only one does), but it's certainly owned by someone.
You might check the ROMs for Atari's "copyright bitmap". It's like 8 or 10 bytes of random gunk, not ASCII or ATASCII or 6502 code, that Atari wanted developers to put into games so that ownership could be proved. Basically they'd ask an offender "Hey, what are these bytes for?" and they'd be unable to answer, because they had no functionality at all and were just there as a signature. (No, I don't remember the bit pattern...)
I wonder if that's the reason Dave Staugas' message exists in the TOS image