Hyperthreading technology simulates additional cores. Your i3 has two physical cores. Hyperthreading simulates two additional cores (one virtual core per physical core). Basically, you have a dual core cpu that pretends to be a quad core cpu.
I agree, a complete mess. Must have had some Nvidia marketers come up with the naming scheme. And I think jimmy you mean to say "only one i5 quad core so far." I'm sure intel will be releasing more chips.