Back in the yesteryears, Microsoft wanted to build a great browser – hence it ensured it was leading the DHTML feature list. Sites began to be developed specifically for Internet Explorer version 4 or 5. At some point however, it realised it had made the browser too powerful – and Google was taking advantage of that, releasing software as service.
Microsoft obviously hates software as service model since it doesn’t tie people down to a particular operating system. People could very much use a Linux based browser (such as Firefox) to access those services, and at the same time share documents with Microsoft Windows based users who could access those documents as well through Internet Explorer.
One of the strategies Microsoft uses to kill competition is to not support their USPs on Windows. Since most users use Windows today, that prevents those USP features to gain acceptance and die sooner or later. It understood that it could not do this with DHTML: obviously because on the one hand DHTML was its own creation and on the other it would break backward compatibility with Internet Explorer. Hence, it decided to at least halt the development of DHTML and has not added any major features to DHTML in the recent past.
Just an opinion.