TV shows are coming on DVD so thick and fast I can hardly keep up! Especially with the multi-season sets.
Star Trek led the way with the TNG box sets and since then every TV show has followed suit. The reason for watching shows on DVD is the absence of commercials and the ability to watch a show whenever you want. Its true on demand TV - and a bonus is the absence of extra fees, good if you love cable shows but can't afford 'em... wait til they come out on DVD.
"Show me just what Mohammed brought that was new, and there you will find things only evil and inhuman, such as his command to spread by the sword the faith he preached." -Manuel II Paleologus
Star Trek led the way with the TNG box sets and since then every TV show has followed suit.IIRC, Star Trek led the way with two-episode discs of TOS. The X-Files led the way when it comes to series; at least, it premiered before TNG.