Revenue deferral is a very strange term. What basically happened is Microsoft claims Windows 10 is free and gives it away to everyone, hence the non-GAAP income. However, under GAAP, they are not actually giving Windows 10 away for free. Instead, they book revenue from Windows 10 but because they aren't charging for it, they must expense it as a promotional activity. What part of this is a revenue deferral? Nowhere, really, except that revenue which should have been booked is not (because it's free).

Microsoft obviously does not want to do this since it drops their earnings by a significant amount, but I'm sure their auditors gave them shit for it. Their auditors probably also made them book impairment charges on things they didn't feel were impaired.