"So if you have 10 people on your team and they own VS Pro with an active MSDN Subscription then you now have 10 CAL's and 10 server licenses"
Does that mean the MSDN subs need to be kept active to keep the CALs?
Most (not all) software in an MSDN Subscription is subject to what's referred to as "perpetual rights" - this means that if you decide to let your MSDN Subscription lapse, then you may continue using the software which was in your Subscription at that time but you may NOT get access to new versions. The TFS server and TFS CAL licenses are part of this perpetual rights software. However, also note that you would not be eligible for an upgrade if your subscription has lapsed. When TFS "11" comes out you would need to buy a new server and CAL, or renew your Subscription.