First off, welcome to our little home on the Web!
(For those who don't know, Mr. Bob Steinbrunn is one of the best aircraft modelers there is ... he also does some darn fine WW I figure vignettes.)
In answer to your question, a "dead track" simply means a track with the shoes linked together under no pressure. When a dead track is laid out on the ground, it will lay flat. A "live track" are linked together with a torque linking the shoes, usually done with rubber bushings under pressure. When live tracks are laid on the ground, they will curl up at the ends because of the torque.
Many modern AFVs have live tracks, which is probably why you have been led to believe the reason is the placement of the drive sprocket.
You've pretty much outlined the reasons for sproket placement -- it is preferred to have them on the end closest to the engine to avoid running the drive train the length of the vehicle and thus take up valuable interior space and raising the vehicle profile (as in the Sherman, the Panther, and many, many other WWII tanks). The Soviets and the British designs, however, went for keeping the drive train as short as possiblet. Eventually, everyone went with this idea .
That is really the only advantage to having the sproket at the front or rear. The U.S. M113 and Israeli Merkava both have engines in the front and so are the drive sprockets -- on the end closest to the engine.
Hope this helps.
