Secondly... SQL Server is by no means required in the stack. We are using MongoDB as our datasource in an ASP.Net MVC app. You can use ANY database.
Similarly, you don't have to use ASPX/WebForms either; a lot of people I know are switching to MVC and not using any of the .net ms usercontrols on the front-end, instead going with open standards and using something like jQuery to handle a lot of the UI and web-service interaction. This is the approach I've taken in recent years, and it makes it a ton easier to create clients for other platforms like iPhone, Droid, etc.
We spent three weeks evaluating Rails, Flask and Django for the app, and the team had experience with all three tools. The risky move to a statically typed, compiled environment paid off because of a solid IDE and good surrounding tools.
Yes, you can use any DB - good point.
Granted, we aren't in production yet... Will see how that goes :)