* top-notch technical talent tends to value equity over W2 income (of which the take-home portion doesn't amount to much in states like CA or NY), people won't give up an equity position at growing company for a higher salary but questionable growth
* for employees that do get a sweet way above market salary package, this creates an incentive to cement their position at the company as much as possible, Yahoo! is probably prime example of that - very little usage of open technologies, all custom-built, all requiring immense institutional knowledge