That only exempts them from the anti-circumvention provisions. Plain old copyright law still applies. A lot of the old games will have effectively lapsed now simply because their owning legal entities ceased to exist, but confirming that poses quite a challenge itsself. Just because the publisher is out of business doesn't mean the game is in the public domain - there may well have been a selling-off of rights during bankruptcy, or another company may have aquired the defunct publisher. Well, let us say you have a game called The Lords of Midnight, published by Beyond Software.
This collection contains EVERY ROM that is currently supported by MAME. Look no further in completing your MAME ROM collection! This set also includes tons of great images and files to heighten your MAME experience including: Screen Snapshots, Marquees, Icons, Artwork, Control Panels, Cheats, and Sound Samples. A varying amount of hard drive space (a complete MAME ROM set would take over forty gigabytes, but most individual ROM sets are quite small) DirectX (Windows version) or VESA 2.0+ (DOS version.
You look it up, and Beyond Software is long defunct. Game good for the taking, right? Well, no: Beyond Software was aquired by Telecomsoft, so you need to look them up too. Also defunct. No, because Telecomsoft (Better known as 'Firebird') was actually owned by BT, the British telephone company, who (AFAIK) still retain the copyright.
That was an easy case, it was all documented on wikipedia and the companies involved are very well-known. Identifying the true owner of something more obscure is a much more difficult prospect. I can vouch for this as me and a programmer friend looked into recreating the days of shareware for the current gen. What we found was a minefield where even if the company closed its doors you had pieces of the company going here and there and nobody knew who the fuck, what the fuck, or where the fuck some 20+ year old game went. The few we did find wanted more money for the rights to distribute the SHAREWARE version of their game than a triple A title from the period could ever hope to make, we are talking about $100K+ for just the limited locked shareware even though we were doing it non profit. That is of course if they would even speak to you, we got many that were like 'Oh we have zero plans for it but we might do something someday' so they refused to allow anybody to sell or distribute the shareware version. The saddest part?