why don't the majority of newer tv shows have a 5.1 soundtrack?
 

i personally think that a show like smallville, nip/tuck, and firefly could have benefited from a 5.1 track, given their nature.

My Theory on way many TV show Set's don't have a 5.1 Track is because I would be too expensive and Time Consuming for the track to be recorded. Plus all three tv shows you noted when they where produced nobody knew if they would sell.

It would probably take up more disc space on these already cramped sets.

Probably because one doesn't exist . . .

That's not a big deal. Lots of movies coming out in 5.1 that originally had mono tracks. They just redo the sound.

My take on why a lot of these shows don't have 5.1 is twofold:

1. It's cheaper and easier to just release them with the original 2.0 soundtrack.

2. They wouldn't really benefit from a 5.1 track unless it was an overly agressive 5.1 track. Many new releases will be in 5.1, and nothing ever comes out of the surrounds, as it isn't called for. Most TV shows would be the same way.