The point of Linux was to bring UNIX to open-source. Linus himself uses a PowerPC, and IIRC, UNIX is x86 only.
You're partly right. Mostly wrong, though
First of all, UNIX was first written in the 1960's, and the x86 architecture is from the 1980's. So you're wrong there.
But point of Linux was NOT to bring UNIX to meanstream. That's GNU. The point of Linux is that Linus wanted to write his own OS for the fun of it, or something, and in the early 1990's he did. I don't think there were any overbearing reasons. GNU and the Free Software Foundation were inventented in the 1980's to write POSIX (Portable OS Interface for Unix, I think) software that was free, and to encourage free software. They had written or ported everything from compilers to editors, but they didn't have an OS. Then they found out about Linus's project, and they paired up with him.
I agree that PS3's running Linux will bring Linux more into mainstream. Or maybe more into center-stage instead of off in the wings, metaphorically. I'd bet a lot more home users will use their PS3 than those who use Linux on their personal computers. I'm not saying it's going to be any kind of revolution, it's not. But this is the kind of thing that Linux was designed for, and what it excels at.