On the other hand they ensured that every Windows user had free access to a high quality browser (at least, at the time IE6 came out).

Well yes, I think with 'decade' GP was referring to everything from the advent of firefox to the introduction of IE9, which might not actually amount to a decade (didn't check). Within this timeframe MS was severely lagging behind in standards, thus requiring everyone to choose between

* support only IE (which they were hoping for of course)

* introduce browser conditionals everywhere

* only use a very limited feature set as the lowest common denominator (leading to table layouts everywhere, using jpg instead of png, never even think about transparency)

This did IMO slow down the development of the web as a whole for quite some time.