Is it just me or the NPCs in Skyrim don't greet each other any longer? All they do is bother my character with the same lines over and over again. I surely enjoyed in Oblivion they were having random dialogue with each other, many instances were funny, or repetitive, or didn't even make sense, but made the NPCs seem to be alive and not particularily just waiting for me. In Skyrim they can look at each other for hours if they are in the same place, but they only talk on a script, which subtracts from the atmosphere... at least for me.

The NPCs do talk to eachother. Try standing around at the Whiterun market for a while. I do agree that they should be greeting other NPCs as they pass one by on the street however. That'd add a lot of atmosphere.

The NPCs make conversations, you simply haven't heard them yet. They're much more colorful than in Oblivion (as the Oblivion's are pretty generic). Now they can discuss their problems. Problem is, they can only discuss THAT problem, so it's as if their problems never go away, kinda makes them look miserable.

I saw a mudcrab haha... there were definitely more random conversations in Oblivion. But I think the streets are more vocal in Skyrim, apart from the preacher in Anvil Oblivion was too quiet... here we have advertising... fine Argonian jewelry!

Aside from limited scripted conversations, they will only react to you getting into a 50 foot radius of them. Worse case of thing is a scripted converstion where a barman and maid complain about a haunted place, even after you've just told the barman it's dealt with.
It does break the atmosphere and immersion. They are more likely to say "What happened here?" to a corpse of someone they killed then say hello to someone in passing.

Oh you should visit Whiterun and try to follow Nazeem ^^ then you will hear that they talk to each other.....

It's just you.

They talk to each other all the time.