Well, I believe MS have some very smart people working for them, and they would have evaluated many products thoroughly before deciding on one. Having said that, I have built several websites in umbraco, and some in DNN, and to be honest umbraco is superior to DNN on many levels, performance, custom development, templating, administration and content management. It’s closer to native asp.net development combined with an excellent CMS which allows structuring of content from within the CMS itself. It provides the core of a website aimed at developers to extend it. Where DNN has lots of pre-built modules ready to plugin very quickly, install a module and customize, quicker to setup with lots of modules, however development is much more complex for dnn.