From what I'm told, the whole StackOverflow/StackExchange 'stack' is based on Microsoft's ASP.NET. SO and the SE sites are probably the most complex that I visit on a regular basis. There's a lot going on in every page - lots of different boxes, pulling data from different places and changing dynamically and responding to user interaction. And the sites work very smoothly, despite the high traffic.
My question is, could this have been achieved using a different platform/framework? Does ASP.NET lend itself to more complex projects where other web frameworks would strain and falter? Or is the choice pretty incidental?