(Then again, could you buy an Intel/UB Tiger disc retail ever? On the other hand, my iMac came with 10.4, and I bought 10.5 with a full license, so in theory I have an available 10.4 license)...
The disks that came with your Intel Mac will only install on an Intel Mac AND only install on the 'type' of machine that the disks came with.
And Apple never sold a 10.4 Intell (only PPC) to the best of my knowledge.
Is that true? I bought an iMac in September of last year with 10.4, then bought the 10.5 disk when it came out. Could I use 10.4 on different hardware . . . . legally?
It's not a matter of legality, it's a matter of compatibility. See above statement.
To get an Intel copy of 10.4 that will install you'd have to get a modded iso from a torrent site.
Its not possible for Apple to add anymore protection to OS X without breaking current macs.
Not true. The could go the MS way of legitimizing the OS. Requiring online validation of CD Keys and getting an Auth key much like installing Windows. This is something Mac users were grateful for Apple not doing.
They could if they wanted to (and it might stir up a few users) put into place said validation and if a non Apple branded machine was used, it would return a "Sorry, buy a damn Mac you moron!" and not auth the installation. Of course hackers would find a way around that as they do with Windows.
So it wouldn't break the current Macs, but would cripple the clones.
Frankly IMO if thats what they had to do, then by all means do it. Flame me if you wish but OS X was built for Apple computers. The same can be said for OS's that only ran on SPARC processors (unix). I owned a hackintosh at one time to get familiar with OS X before I bought my iMac, I'll admit it. Then took it off once I bought my iMac. I gotta tell you it was hell getting it set up.
OS X was built for Macs, let it be. Otherwise bring back the PPC processors then there wouldn't be any problem of clones.