The assumption in these threads tends to be "we could run amiga OS on any PC and it'd be rad". And that would rad, but it won't be reality.
Absolutely - I'd love to see AmigaOS4 running on a cheap x86 machine. But it's simply not practical.
What you say is true. I certainly don't disagree. But leaving it on PPC is even less practical. You need developers to build your code. For that you need money. To do it effectively, you need lots of money. Selling PPC machines to 10 users at 1500$ a pop ain't gonna do it. Selling x86 machines to 500 users at 300$ a pop stands a better chance. And the lower the price, the more likely you will sell it to more users. This too is reality.
So, for many of us here, the argument ain't "doing x86 is rad!" Instead, the argument is "doing PPC is suicide!"