Joe knows from where he speaks. A closed track loop allows the signal to cancel itself out because it travels in both directions from the feed drop(s). In the case of a track with a single feed (should be at one end), you still may get feedback when the signal hits the end of the track and bounces back which cancels out the signal. Basically, you have to look at DCS (and DCC) the same way you'd look at a packet network like the old "thin net" Ethernet and put a "terminator" at the end of the buss (track). DCC uses the term "snubber" which is the same as the "Deats Filters". In a three-rail context, the snubber/terminator/Deats filter would connect to the far end of the track and the feed drop on the near end. For this exercise, dismiss the internal resistance of the rails but suffice it to say, the longer the track block, the greater the resistance and the lower the requirement for a snubber at the other end. This isn't an exact one-size-fits-all, but basically it's a resistor and capacitor across the power leads to act as a terminator (which is what was in the old thin-net terminators).
Also, track joints will affect signal quality and Barry and I had discussions about the pros and cons of soldering track joints and its impact on block lengths. They key to remember is use a single feed per block and you want to terminate the tail end of the buss or track block (but only if you're getting bad/weak signals).
