It's not uncommon for sitcoms to have similar characters. There are established archetypes that just work. Of course, nitty gritty details will vary from show to show, but more often than not, many characters will share a vast majority of their personality with another. Almost like endless parallel universes, almost the same, but there's always something that's just a little bit off. Take Ross from Friends, and Ted from How I Met Your Mother for example. Both relatively uptight with a bit of an ego, but in the end, they both get the girl. There's Joey Tribbiani and Andy Dwyer. The list goes on.
One of the most glaring pairs however is Kevin Malone and Norm Scully. Both are a bit lacking in the brains department but they still have little flashes of genius. They tend to be the butt of most jokes in their respective workplaces, and if there's a way to fly under the radar and do the bare minimum, rest assured they'll find it. When it comes to food however, their genius knows no bounds. Take Kevin's pie math, or Scully's encyclopedic knowledge of every hot dog vendor in New York City. When it comes to their grub, these boys are no slouches.
The similarities are so striking, that many of their lines are interchangeable and it can be hard to differentiate the two. How well do you know your paper salesmen from your NYPD detectives?