>Can someone explain what's the benefit of doing it that way?

Keeping out the riff raff? Those videos are targeted at Mac developers, not people having issues with Safari and/or iTunes.

>I'm on Windows (Ubuntu also, in a VM) running Chrome. Sure, I could install Safari or iTunes, but why do I have to?

Just because those are the prerequisites Apple made for watching them.

That said, I think you can also watch them without Safari for streaming (you just need Quicktime IIRC), but downloading them needs iTunes.