It's not necessarily their true market value - it's just their value to Microsoft at that particular time.
If the project that they're working on is strategically important, and any disruption is unacceptable, it might be in Microsoft's best interests to pay them well above their market rate to ensure nobody quits. But the same engineers in another part of the company may not have received raises at all.
On the flip side, Google may be willing to pay above market value in order to take valuable assets away from their direct competition in key areas.
Just because one company in one circumstance pays them a certain salary, it doesn't mean that's their true market value, unless they could get the same rate elsewhere if they quit tomorrow.
Agreed. Most companies realise the disruption caused to a project when key staff leave and paying an extra 10K, 20K or even 60K passes a simple cost-benefit analysis - but only during that project.
Personal experience: I was one of about 5-6 people who actually knew what they were doing on a 50 person, 3 year project at a large company when I got a much better offer from a much better company. I called the HR manager in good faith to see if they would match it, but he didn't want a word of it (nearly hung up on me, in fact). That was until he was told by my boss that I'm needed on a critical project. Not only did he call me back and talk to me, the CTO of the company (who never spoke to me before) spent an entire hour with me, ignoring his constantly beeping phone, convincing me to stay. As flattering as that was, I knew by then that they only did this because of the critical project and took that into account in making my decision.
I still decided to quit. The "critical project" was cancelled two weeks later (for unrelated reasons).
If the project that they're working on is strategically important, and any disruption is unacceptable, it might be in Microsoft's best interests to pay them well above their market rate to ensure nobody quits. But the same engineers in another part of the company may not have received raises at all.
On the flip side, Google may be willing to pay above market value in order to take valuable assets away from their direct competition in key areas.
Just because one company in one circumstance pays them a certain salary, it doesn't mean that's their true market value, unless they could get the same rate elsewhere if they quit tomorrow.