In a reasonable world, this would be the rule: If the original author/publisher is no longer supporting the software for a certain hardware configuration (practical or commercially emulated), then it is considered abandoned. Share and enjoy.
Example: Photoshop for Intel Macs running Mac OS X is currently maintained by Adobe. Purchase it. Support the publisher. However, Photoshop for PowerPC Macs running Mac OS 9 and earlier are not supported by Adobe. Sharing this particular configuration of the software will not affect Adobe. They are not actively developing or supporting it.
The main question to ask is this: Would the original author be financially affected if the software is copied and shared? If the answer is "Yes", then do not copy and share. Buy it. Register the shareware. Support the author. If the address in the 'Read Me' is obsolete, Google the author's name and try and see if he or she is still developing.
As for the Pac-Man example, the above "rules" would allow sharing of Pac-Man game programs on unsupported hardware. Does that mean the user has a legal claim to the Pac-Man IP? Of course not. That's not the implication at all. However, usage of the game program on obsolete hardware isn't going to affect Namco's bottom line. Pac-Man for the Atari 8-bit computers, for example, is dead to them. They have no further financial stake in it.
*This is coming from someone with a hobbyist programming background and who purchases physical copies of old, unsupported software, including Adobe products. Hey, I like physical media!
Example: Photoshop for Intel Macs running Mac OS X is currently maintained by Adobe. Purchase it. Support the publisher. However, Photoshop for PowerPC Macs running Mac OS 9 and earlier are not supported by Adobe. Sharing this particular configuration of the software will not affect Adobe. They are not actively developing or supporting it.
The main question to ask is this: Would the original author be financially affected if the software is copied and shared? If the answer is "Yes", then do not copy and share. Buy it. Register the shareware. Support the author. If the address in the 'Read Me' is obsolete, Google the author's name and try and see if he or she is still developing.
As for the Pac-Man example, the above "rules" would allow sharing of Pac-Man game programs on unsupported hardware. Does that mean the user has a legal claim to the Pac-Man IP? Of course not. That's not the implication at all. However, usage of the game program on obsolete hardware isn't going to affect Namco's bottom line. Pac-Man for the Atari 8-bit computers, for example, is dead to them. They have no further financial stake in it.
*This is coming from someone with a hobbyist programming background and who purchases physical copies of old, unsupported software, including Adobe products. Hey, I like physical media!