No you're totally off base. Apple made an engineering decision to use Intel chips because motorola technology was seriously lacking, hindering Apple's competiveness. Thery didn't switch to Intel so that cheapskates could push the OS on to other cheaper hardware. Otherwise, we'd still have motorola and your arguement is bogus.
Since when was my argument talking about the PowerPC to Intel switch? I was just arguing that Apple cannot arbitrarily ban legally-purchased copies of OS X from compatible hardware just because they did not make the hardware. Apple could have been equally as vulnerable from such a suit if they were still using PowerPC CPUs and they actively stopped you from using OS X on a third party PowerPC-based computer. The only reason why no such suits ever came up is because practically no one used PowerPC in the consumer space other than Apple -- i.e. there was no third party PowerPC market there to MAKE the third party hardware.
As for your AT&T example, that came down to the fact that the telephone system was part of the national infrastructure. You can't have seperate telephone networks which would limit who you could talk to, which would have a severe impact on everything from safety to commerce, etc. You can argue the internet, but hey windows PCs work just as well as macs online (well, ok, I am just illustrating a point)
The reason why AT&T was forced to open up was actually not because it was part of the "national infrastructure" but because AT&T was not allowed to arbitrarily limit what I could and could not use on their network. As a paying customer of the AT&T phone service, the court ruled I was allowed to use whatever phone I wanted to with that service so long as it didn't interfere with the network. I'm the consumer and I can do what I want with your product is what the court ruled; you cannot make my decisions for me.
Apple doesn't own the intenet. They make the telephone in this case, except the telephone needs software to make it run, hence they make the software too.
If this is the way you took the AT&T example, then you've seriously misunderstood it. In a proper analysis of this example, Apple is both the phone network operator (in this case, this network is Leopard/OS X) and the phone manufacturer (in this case, the actual computers themselves like the Mac Pro, MBP, etc). Apple currently says, like AT&T did, that you cannot use any other non-Apple hardware with their 'network' (i.e. Leopard). AT&T was told in the 50s that this type of behavior was illegal, and that they had to let other manufacturers build hardware too. Should the court rule correctly, they will also find that it is illegal for Apple to limit the use of their 'network' to only their hardware and that companies like Psystar must be allowed to build computers for Leopard.
If MS decided tomorrow to build their own box and limit windows to their hardware, they should be allowed to do it.
That statement just proves that your argument is not based at all in United States law but is only your opinion. No, in fact, Microsoft would not be allowed to do that as they would be declared a vertically-integrated monopoly and broken up into pieces like AT&T was by the US Justice Department. Disagree with that all you want, but it's the law in the United States. Full stop. If you want, you can run for election in the Senate and change the monopoly laws, but until then the law of the nation just doesn't allow for that. They won't allow for Apple's vertically-integrated practices either in this case.
EDIT: Also to your argument about having to support third party hardware, that's entirely baseless. Apple can just declare that their warranty does not cover those who use their software on non-Apple hardware, and that's perfectly legal. In other words: GM cannot legally stop me from crashing my car if I want to, but they sure aren't liable for me doing so. They say that in the warranty that they're not liable, and that's perfectly legal. I as the consumer choose to take that risk. Or, to go back to my AT&T example, AT&T was never asked to provide a warranty for those third party phones and they were never liable to. It was at the discretion of the customer to use those phones. AT&T never had to help those customers.