Mac OS X runs natively on the Intel hardware. This is the power of using an open operating system. Most of the work of getting the BSD and Mach underpinnings of Mac OS X were already functional on Intel, so getting the whole system to run on multiple platforms probably involved relatively minor tweaks and recompiling.
In contrast, it took years for them to get the entire Mac OS running in native PowerPC code when they made that switch.
My guess is that this is explained by two things. First, the Mach and BSD code already ran on Intel, so they could rely on a lot of existing work. Second, emulating the PowerPC processor on Intel chips would be prohibitively slow.
Open source software gives a lot of freedom to people, and that freedom pays off not just in personal capabilities, but for businesses.
I do my writing in LaTeX, using BibTeX for citations. I like that because I know that it will be possible to typeset a document I write today in decades, and it'll still look just as good as it did when I first wrote it. If I have a problem, I can fix it, either in my document or by changing the programs.
I don't trust Word or Powerpoint. The formats keep changing, they keep adding useless features, and if I have a problem, there's really nothing I can do.
My guess is, Apple felt the same way about the PowerPC platform. It was elegant, beautiful and not keeping up. So long as they were tied to all of their history with the legacy of Mac OS 9 (which incorporated code going back decades), they couldn't make dramatic hardware changes. Now that they have an open system, they can do as they like, and make it work.
There's also some new software, but nothing that made me sit up.
“Changes” by Phil Ochs from the album Phil Ochs In Concert (1967, 4:40).