Then put MySQL on a Linux box, no need to have it on Windows...

And then you have the added complexity of two OS platforms to support.....

I think they made the point in the article that they could have overcome the obstacles of the ASP MVC platform, but why? They said they're more productive on Rails, they like working on it better, and it's cheaper.

What positive would there be (for them) of staying on the MS platform?

How many mixed platform server shops do you know of? If you're going to go linux/OSS for your DB you might as well go all the way.