The draw of using a DSLR is the large sensor and the interchangeable lens system behind it.
However, the "conveniences" of Auto-focus and auto-exposure are better on dedicated videocameras then on DSLRs.
For consumer video purposes (not "film-making" as I recently debated with a member on this forum I'm sure others weigh in soon enough), a dedicated video camera is more cost and time-efficient in my opinion.
That's not to say you can't make good video with DSLRs. But it's a deliberate choice with some limitations that potential owners should explore more fully.
Having video capability doesn't inhibit the cameras still-capture in any way. In fact, one could argue that video was "bolted on" - witness the relative lack of integration and controls in the early models such as the D90 and the D300S.