During old days sales, programmers and tech folks need to run several instances of OS, including server platform with mobile capability, so the memory, CPU and disk requirement for notebook was really high - Booting up the machine and fire up virtual machines would take 30 minutes before we can do or work / presentation.
Back then machine reliability is not really important - since we are using virtual machines the dependency wasn't so heavy, and we can always make it work in a new machine in like 2-3 hours.
Now the speed and such is much improved, but business world no longer require them - with remote computing needed is a WAN connection, and we get all the computing powers over the line :P
Now powerful desktop / machine is more for personal usage. How ironic.
The only exception would be lock down corporate machines which has like 20 thousand pre-installed apps, 20 million policies to run, and those machines still stuck in like, Windows 2000, and hmm... P3/P4? I worked in such a environment. Everyday I fired up my machine, go for my breakfast, toilet break, and the screen ain't ready for log on yet. There are people who left their machine on 24X7 for this sole reason, and I didn't want to do it because it would really cut down your machine's life span.
Vista brought back those horrible memory.