5? Maybe I don't watch enough TV, but I'm struggling to think of even one modern comedy that looks like it'll become a classic in the future...
I think this is partly down to the fact that TV shows aren't made to "last" anymore. You need to be really great to get a 2nd or 3rd season commissioned these days, so perhaps the focus is on getting those ratings - and not really worrying about longevity from the outset.
The other issue is that there is FAR MORE competition in terms of entertainment these days.
It was easier to create a cult classic back when TV shows were battling against a handful of other channels, and didn't have to worry about the internet, YouTube, game consoles etc...
Having said that, I don't think the quality of TV shows has dropped at all. If anything, the uber competitive environment has meant everyone has had to up their game in order to survive!
Modern Family and It's Always Sunny in Philadelphia have made a real impact lately. I'm a big fan of New Girl too.
Obviously Family Guy and South Park are pretty epic, do those count?