What DSLR do you have? Also, part of the problem is that you're only using Windows Movie Maker. That program KILLS quality of video ten fold. If you have a T1i or a T2i then you need to be using a program such as Sony Vegas or another one specifically for editing video. Especially because WMM can't handle full 1080 HD videos.
Incorrect. Most film crews use DSLRs for a lot of their shots because of the easy of use, and the high quality. See my above post.
Again, incorrect. See my post at the top.
I shoot with a manual focus Nikon D90 and it shoots GREAT HD video. It's all about what programs you are using. Again, this is coming from a Nikon guy.