I've worked in both the open source world and the closed source (dot net) world. In my very humble opinion, the dot net world just doesn't need the amount of online help that the open source world needs at least not from StackOverflow. Dot Net and it's kin tend to have very good help out of the box and extensive documentation. This is very much unlike in open source where honestly, it's not even possible to install an operating system without having another computer available online.
Again, I'm not dissing open source here. I've learnt a whole lot from it. But there's many, many things that are lacking in open source, which when seen from the other side seem extremely basic and fundamental to creating good software.