It's part of the mythology of American capitalism: if they're a big winner, they must be a big innovator, because innovation drives the economy!
Don't get me wrong, I love American capitalism, and I don't think innovation trumps all other factors (like reliability). The myth of Microsoft innovation is just one of those peculiar cultural myths that, in this case, blocks out the reality for people who don't work in the field.
Reliability trumps innovation if people want to use the same stuff for a long time. In the consumer market it seems it's all about new stuff. People chuck out perfectly serviceable items because there's a new model they want. Which companies would bother to make a reliable mobile phone or computer for the mass market.
The facade of innovation works for larger items too. Why create a vehicle that lasts long after the 5 year bodywork warranty when you're just reducing your market. Entice people with the new model, make sure your goods don't last too long - that appears to be the capitalist way.
Don't get me wrong, I love American capitalism, and I don't think innovation trumps all other factors (like reliability). The myth of Microsoft innovation is just one of those peculiar cultural myths that, in this case, blocks out the reality for people who don't work in the field.