I think that the reason Laurel and Hardy, the Stooges, etc are deemed funny, while newer imitators are not is that when THEY did it, it was new, original, unexpected and groundbreaking. The newer guys who did the same thing, for example Soupy Sales, come across as kind of lame, somehow.
However, what was funny in the 1920's, 30's, 40's and 50's doesn't always translate well into modern comedy. Part of the reason is that as our society and culture changes, what that culture finds humorous also changes. I've seen 'Ma and Pa Kettle' films made in the '40s and 50's, and don't find them very funny, although they were successful enough in their day to have a long string of sequels, I forget how many they actually made. Other films from the same era hold up much better, for example 'The Egg and I', 'Bringing Up Baby', etc.
There are lots of good modern comedians (Ok, I'm going to include people from the last 30 years or so), such as Monty Python, many of the members of Saturday Night Live, Jerry Seinfeld, Steve Martin, etc, who have contributed so significantly that they have actually changed the language. See how many of the following references you recognize:
Are you "spongeworthy" or do you know someone who is?
Are you or someone you know a "wild and crazy guy"?
Did you ever experience "shrinkage"?
Have you ever gone to an "argument clinic"?
What is the airspeed of a swallow carrying a cocoanut?
Have you ever worked for "Van deLay Industries"?
Do you need "The Bro"?
Are you employed as a lumberjack, and is it really OK?
Have you ever owned a "Bass-o-matic 76"?
What does a castle full of virgins do on stormy evenings?
What was referred to by the speaker who said "They're real, and they're spectacular"?
Are you "master of your domain"? Really?
"I'm not dead yet!"
There have been many good comics come up in recent years. I recently saw "School of Rock" and found it hilarious. "Lost in Translation" showcases Bill Murrays talent. There have also been many good shows on television, some of which lasted, others not. I found "It's Like, You Know...", "That 80's Show", "Andy Richter Controls the Universe", and "Coupling" to be very funny, yet all were yanked before developing much of an audience.