Williams Pinball ROMs include a license that explicitly limits their use to the supplied Williams hardware.
Which is interesting b/c (I won't post the link, but) I can go to Williams official website and download most of their pinball roms with no questions asked.
And if you click on the link to any of those ROMs, you get the license agreement, which reads (in part):
1. License. The software installed through this process (the "Software") and any related documentation provided to you are licensed to you by Williams Electronics Games, Inc. or its affiliates ("Williams"), subject to the terms and conditions in this License Agreement. Williams retains title to the Software and related documentation. This license allows you to use the Software
only in the specific pinball games manufactured by Williams and marketed under the WILLIAMS or BALLY trademark for which the Software is intended ("Pinball Games"). To do this, you are permitted to
transfer the Software into a Flash ROM device in the Pinball Game. Other than the copy of the Software installed for you during this process, one (1) archival copy thereof, and the Flash ROM copies for installation into the Pinball Games,
you may make no copies of the Software. You may not transfer or sublicense your license rights in the Software to another party or distribute copies of the Software, except that you may install Flash ROM copies of the Software into Pinball Games owned by others as part of servicing such Pinball Games, provided the owners of the Pinball Games read and agree to accept the terms and conditions of this License Agreement and provided you do not charge an additional fee for the provision of the Flash ROM copy of the Software. Under no circumstances may you sell copies of the Software, including Flash ROM copies. You may not publish the Software.
(Emphasis in the previous paragraph added by me.)
If you steal someone else's IP, I believe you can only be prosecuted to the extent that they can show loss of revenue from the infraction - i.e. in the case of arcade roms, if they really wanted to, the IP owners could probably come after us for the value of an arcade board containing the ROMS on E-bay (minus the value of the other chips on the board) so usually $10-15.
Yeah... it's the people distributing the ROMs that they really care about, and even then it's usually just a cease-and-desist.
--Chris