Partially. I don't think the entire market was headed towards all-in-one - that's an Apple thing (and others kind of follow suit when they see how Apple do it).
It's not about a straight comparison for the time - they have to look at the future of each platform and plan ahead. They probably know what they're doing for the next 5 years.
If they stuck with PPC, the laptop line would be much more stagnant. When they introduced OS X, they probably had plans for going either way (researching processor independence, compiling for all types etc), and as it approached 5 years in, it was becoming increasingly apparent that PPC wasn't going to take them where they wanted to go, whereas Intel could.
The transition was actually REALLY fast and efficient, due to all the planning. The rabid Apple fanboys also played a part in quick adoption - they introduced new designs into the intel MacBooks for example, and changed the names. A swift efficient cross in marketing. Pretty amazing, really. Aluminium iMacs weren't far behind.