Why would that be? I suspect that's more because the pool of people I know is biased than because the pool that posted is biased -- some orgs in Microsoft will match offers from other companies even though average compensation is relatively low, so if you're new and you know a lot other people who are new, the sample of people you know is probably biased high.
To be clear, I think that's bad both for Microsoft and for Microsoft employees. I'm just trying to figure why the Microsoft data is anomalous relative to the numbers people have personally told me. The reason it's bad for employees is obvious. The reason it's bad for the company is that it's pretty common for people who have been here a long time to shop around, find out that they can make much more elsewhere, and then get a matching offer from MS. Once word gets around that the best way to get a fair raise is to interview elsewhere, people start interviewing elsewhere, and some of the people who interview are going to leave, even if that wasn't their original intent.