I don't mean to be a wet blanket, but no way was this due to the shift to Linux.
At least, there's no way I can imagine it could be. I've got tools that run on both Solaris and Linux, and there's not really that big a difference.
It's got to be the hardware.
The $50k servers were probably two years old or more, and were replaced with brand-new boxen.
I do think Linux is good, don't get me wrong. But this is a *highly* misleading intro.