Re:Tag line from the theatrical trialer: (Score 4, Informative)

Actually there IS a need to install the CDs, as not all TBC content came with the patches (I suspect mainly the Outland regions). Don't know how it is in the US, but it's like this in the europe. It is true it will re-run a few patches after installing though.

And yes, you can play the non-TBC regions with a normal unupgraded client even if you have activated TBC.