The reason you don't get it is because most of the topics that Seinfeld was based around are moot points in 2009.
The various complications, misunderstandings, social disasters (yada yada yada) of some of the show's most classic episodes don't exist or are not funny due to the many technologies that have proliferated since Seinfeld went off the air in 1998.
Cell phones
"The Sponge," from the show's seventh season, is best remembered for coining the term "sponge-worthy." Although, the episode's funniest moments involve George (Jason Alexander) fretting about being cut "out of the loop" after he tells his doomed fiancée Susan the truth about Jerry's pants size. What's even funnier is that the main characters are constantly out of each others' loopsto the extent that episodes like "The Movie" are entirely dependent on the principal cast's inability to get a hold of one another. Of course, that wouldn't be a big deal in the age of cell phones, where George, Elaine (Julia Louis-Dreyfus) or Kramer (Michael Richards) could just let Jerry know they're going to another theater via text message. And while George is such a miser that he'd likely be one of those jerks who prides himself on not having a cell phone, a large chunk of his development as the show's major fussbudget would be lost if, in "The Chinese Restaurant," his girlfriend Tatiana could call him directly. George is dumb, but he's not dumb enough to answer his own phone as "Cartwright."
Caller ID
By the time "The Susie" aired in February 1997, caller ID was a readily available technology. But taking George's stinginess into account once more (he did let Susan buy potentially toxic envelopes for their wedding invitations just because they were cheaper), it wouldn't make sense for him to shell out the extra cash to screen for a potential break-up call, not when an answering machine could do the job. With caller ID now as standard a phone feature as the handset, George would definitely know if it was Jerry or Allison callingand no one born after 1983 would know the "Theme From Greatest American Hero (Believe It Or Not)."
YouTube
If a comedian as witless as Jeff Dunham can have the seventh-most-watched video in YouTube history, then surely a fictionalized version of Seinfeld (the guy who perfected observational humor) could knock Avril Lavigne's "Girlfriend" out of the top spot. Hell, he could even use it to launch his long-in-the-works pilot Jerry. Bam: Seinfeld's greatest meta-joke destroyed by the Internet meme machine.
"The Boyfriend"'s nod to Oliver Stone's JFK wouldn't work well in the YouTube era, eithernot that the "back and to the left" gag has aged particularly well to begin with. Applying some Jim Garrison-style analysis to the episode's Zapruder film sequence, we see a man (who must be Orville Nix in this situation) filming Kramer and Newman (Wayne Knight) as they get assaulted by someone they assume to be New York Mets first baseman Keith Hernandez. If you recorded a World Series champion (or two champions, if you support Jerry's "second spitter" theory) hocking a loogie at a fat guy and his gangly friend with a goofy haircut, wouldn't you upload the video to YouTube (or Vimeo and Daily Motion) as soon as you got home? Newman would have seen the video that very night, vlogged about it, and redirected all his Hernandez hate at Jerry.
Keyless entry
Cosmo "Let's install a hot tub in my apartment" Kramer is George's polar opposite in money matters; so you'd better believe any car he'd buy would be equipped with remote-control keyless entry. And he wouldn't cheap out: That baby could trigger a panic signal from any level inside "The Parking Garage." That still doesn't guarantee the car would work once he finds it, but that's the kind of problem cell phones were created to solve. (Seriously, the "show about nothing" would be less so if these characters had cell phones.)
Decider
We're not saying our colleagues in New York would list an appearance by a white supremacist at Madison Square Garden, but there'd probably be a Gag Reflex that would let Jerry and George know not to swipe a car reserved for said white supremacist, which they do in "The Limo." Similarly, Decider's movie listings would eliminate the B-story in "The Pool Guy" where Kramer pretends to be the voice of Moviefone. If this article proves anything, it's that Decider is great at making Seinfeld less funny.