"getting an MBA and climbing the corporate ladder" - one would have thought in Tech companies Engineers would count for more than MBA's, but clearly that's not the case with Yahoo.
However, in a Tech company the contribution and therefore compensation of an Engineer would be expected to be higher than that of an MBA.
http://bhorowitz.com/2010/04/28/why-we-prefer-founding-ceos/
There's a lot of small intangible things that go in to making a huge successful company. The core employees "wanting" to work at the company (as compared to just collecting a paycheck) is one of the most imporant ones.