I have heard that it will take more than fours years from now till all seasons are released on DVD...
Anyways, it is taking a lot of time watching the DVDs I've already got: First I watch one episode enjoyng the clear picture quality (even though I have seen all episodes uncountable times before), then I watch it with the "nitpicks" subtitles. Some episodes even has commentaries, which means that I have to watch every episodes up to three times...
BTW I don't think the DVD-format will survive 4 years...