legal terms make my head hurt...

[makkuwata]

http://www.copyright.gov/1201/

(3) Computer programs and video games distributed in formats that have become obsolete and which require the original media or hardware as a condition of access. A format shall be considered obsolete if the machine or system necessary to render perceptible a work stored in that format is no longer manufactured or is no longer reasonably available in the commercial marketplace.

does this mean roms for old systems are now legal, in america at least?

[Papercut]

This only dictates that software for obsolete formats may be:

[exempt] from the prohibition against circumvention of technological measures that control access to copyrighted works.

Which means you can hack away to your hearts content, but the software itself may still be copyrighted.

Also how to determine a format to be:

no longer reasonably available

is not clearly defined. I would guess that if Nintendo decided the NES was still reasonably available (say via e-cards or second hand) that would stand.