KAH9158

I currently have a standard definition TV and analog cable. I want to buy a high definition TV and get digital/high definition content. I see that my cable provider (Comcast N.J.) and the satellite providers have offer very few high definition channels. They only offer the local stations and Discovery and ESPN in high definition. I understand that the channels must create the high definition content and provide it to the cable/satellite companies before they can offer it. My questions are these. When will most of the channels offer high definition? As more channels offer high definition content will the cable/satellite companies offer it immediately, or do they have technical limitations?
In short when will most of the channels be available to me in high definition? I realize that television shows/movies that were produced in standard definition will never be high definition.

Thanks