Well, it's just an Internet poll, not an official list.

It's just for those of us who like polls.
Think people who vote there come mainly from Internet biggest fandoms, that's why most shows are modern. Anyway, there are still a lot of older shows in the top 40, like Bonanza, Gunsmoke, The Man From U.N.C.L.E, Laramie, many of the Star Trek shows, Scarecrow and Mrs King, Les Filles de Caleb, Scoop, Trapper John MD, Little House on the Prairie and Combat!. Other shows aren't that old but started airing before 1995, like The X Files, The Simpsons or Northern Exposure.
Twin Peaks is rather high in the nominations poll at the moment (1106 votes). Just a cruious fact.
I won't say whether the shows in that list are good or not - I really like some of them, I dislike others, and I have never seen many of them. But I guess if someone votes for a show it's because of a reason, whatever it is.
Psych is in a very low post at the moment, but it's started to get votes. I just thought it would be nice to vote it a little so it would get higher in the nominations and eventually could join the top 40. Well, anyway it's up to you, if you want to vote, then vote, if you don't want, then don't.