With respect to multiple terminations on one circuit (capacitor/resistor), isn't that effectively what happens when you use a plugin filter in each socket?
I would also be intereted to discuss that point, as I am inclined to agree. Or have we discussed it elsewhere?
I did once encounter a real problem caused, in part, by a house builder that had fitted a second master socket. The thing was, in addition to having a second master, the builder had also managed to accidentally swap the line pair between the two sockets. This leads to the two capacitors in series shunting the pair, via the ring wire in the middle, with no series resistor. That was pre DSL, but it pretty much killed dialup modem connections too, even the voice audio sounded muffled.
Also shunted by two resistors of course, but that was fairly harmless, it was the cap's that did the damage.