I don't think many (any?) engineers from Google or Facebook would jump to Microsoft for higher pay. If money was the one motivating factor then surely said engineers would be working in finance rather than at Google or Facebook.
Thought experiment for you: what fraction of current salary would it take to get a current Googler to flee the company? Would they still do the work for $30k rather than $150+stock?
No company with with an HR department is going to their average employee over $100k without a business reason.