Theres some misinformation here, so I will try to clarify (and also show up the idiocy of laws in the US specifically).
1). It is LEGAL in the US to backup software that you own, so as to preserve it in case of damage. You are only allowed to keep a copy for yourself, not to give to others.
2). It is ILLEGAL IN ANY WAY to modify a computer program, as this is termed as HACKING. You are ABSOLUTELY by LAW not allowed to do this!
So one law says you can copy software, but sometimes the only way to do so is to modify the software concerned. A quandary, a double whammy, a load of crap basically! A really well thought out set of laws!
On the subject of Abandonware, lets get some things straight:
1). A disclaimer (i.e. a site saying "we dont condone you doing this, blah blah") is in itself bullshit! No court in the world will uphold a disclaimer. If its illegal to do something and you try to cover your back, you will be prosecuted. To coin a phrase, "a disclaimer isn't worth the paper it's printed on".... FACT!
2). Unless the author owns the game outright (many sold their titles in full to the publisher), and gives permission, that copyright is theirs for 70 years, and at any time, they can prosecute any site that holds images of their property. The same for software companies, as long as they haven't been made bankrupt, any ex head of a company can file to prosecute.
3). All games for as long as I can remember have always carried the statement. "Not to be copied, hired, lent, stored in another media or a retrieval system" That includes the internet, as its another medium from the original computer system, and its stored so it can be retrieved.
4). Ocean sold Chase H.Q. Ocean (infogrames) can prosecute you. Taito own the license of Chase H.Q. Taito can prosecute you. Teque London programmed the game for Ocean. If the music in the game was copyright Matt Furniss, HE can sue you.
At any time, any of the authors of the games can prosecute people.
Abandonware is a nice title, but the majority of the sites have no business distributing software they 'think' is no longer profitable. The GBA is the reason why the Bitmap Brothers won't allow any of their Amiga back catalogue to be distributed free. Why bother buying the pixel perfect rendition of the Amiga original (and the reviewers will certainly mention the Amiga), if you can download the Amiga emulator and the game?
I think one of the few LEGAL Abandonware sites is Cinemaware, Factor 5, and not much more.
Abadonware is a quaint little concept to give piracy a more acceptable name, because lets face it, in the majority of cases, you have to use illegally obtained software to use with emulators, which is all born from piracy.
Just for the record... I actually don't give a toss, which is obvious by my history
