It has nothing to do with download size. The reasons are entirely political/legal. It's complete BS as far as I'm concerned. You can develop some great applications in .NET but can't be ensured that everyone will have the framework installed. Then you have to deal with bootstrapping the framework install which just makes your app installers huge. grrr.... I don't know the details but have heard from very reliable sources from within MS that this is the case. Good thing I do all of my .NET development for intranet applications where we can have the nice IT department just push it out. Anyway, it will be included by default with Longhorn but until then we'll just have to deal with downloading it.