DRM is Digital Rights Management, which, very basically, are technologies that try to prevent piracy by restricting features and capabilities (to prevent copies without authorization). The open nature of Maemo is exactly the opposite. Try giving a look to DRM in Wikipedia, it is a widely debated issue, often it has been called the biggest tech failure of all times; and also a feature so wanted by the industry, that has been pushed so hard, and the most hated by consumers.

If the N900 is compatible with Maemo 6, then good chances are that games will happen there. But it is not going to happen soon.