When was this, exactly? IIRC, the PPC macs are the ones that were actually better at it. Nowadays it's a tossup. Most recording schools teach both platforms. Linux is gaining ground as well... SAE even had some open-source stuff in their curriculum for a while.
Power PC chips were rubbish and IBM could not produce them fast enough for the expanding market share. The switch to x86 was a very smart move by Apple. PPC is really only super beneficial in very closed and embedded systems, like consoles or platforming servers.
What a school teaches and what a business uses is not mutually exclusive. The reason studios buy macs is because the overall cost of ownership is less than a PC. Most studios will use the same Mac rig for 5+ years at full capacity. You won't see many PCs lasting 5 years with out upgrades, because Windows is the worst OS at managing resources.
Open source. Meh, the problem is crappy driver support, and the higher level of knowledge needed to make things work. I don't see you dumping a ton of money on digi or even like motu hardware sets and try to get open source drivers to maybe work, when they work native in OS X or Windows.
The main studio I worked at a lot had a 1st gen Xeon Mac Pro, which was out in 2006. 4 years later they are using the same hardware, with zero problems and zero hardware upgrades with the newest software with no performance hits. They will probably get another 2 to 3 years out of it before they need to buy a new system. Sure, they dropped like $3k on a high end recording rig, and yes my buddies that recorded there had songs with well over 200+ tracks of audio on it, but it performs like a champ. Try to do that with a PC and have it last 6 years, and have zero down time. Of course that studio stiffed me on my last invoice so they can die in a fire now, and I don't care if their crap breaks anymore because they owe me money, but that is beside the point.
Plus, Windows has one single point of failure called the registry, which is dumb from any efficiency standpoint you look at.
I'd like to see lots more Linux and Unix users out there, but with my latest experience trying to get HDMI audio out to work in Linux, I highly doubt I see any audio engineer try to go through what I did to make it work, and my audio still is not working 100%. I had to manually compile drivers and install them, which while not the hardest thing in the world, but how many music engineers are going to play at the command line? Linux lacks there with out of box support for hardware, that is just the truth of it unfortunately...