Trying to understand OSX's Activity Monitor and how cores are monitored.

I'm using Lion on my work Mac Pro (2.66 quad Xeon) and I just noticed that when I use Activity Monitor, it only shows 1 bar when I track usage in my dock. My Macbook Air with dual core (?) i5 shows... 4?

So my question is... what's going on? Why would a Quad Core Xeon only show 1 CPU Activity bar, and why would my non-HT i5 Dual Core show 4? Is it because one is Lion and the other is Mavericks and there were changes made?

For my MBA, since it's dual core... shouldn't it only be showing 2 bars? I was under the impression that the only way it could show 4 active bars is if it was capable of hyperthreading.

I seem to have a lesser understanding of AM than I thought I did.