Well, it's not really correlated to them being new (unless you factor in that buying a used device will cost less).
As said, both poly aftertouch and 14-bit controllers require more (possibly expensive) circuitry, which I suppose is the reason from them only appearing in the more pricey range. And in the case of 14-bit controllers, I guess there might have been other technical restrictions (memory limits and the like?) which prevented manufacturers from using them in the past. The need for 14-bit controllers mostly arose with the advent of plugins, I think, since using a 14-bit MIDI controller to program a hardware synth that only has 7-bit input anyway would be pointless - but with plugins, you have a practically unlimlited parameter resolution, so 14-bit controllers are becoming more common.
Just taking my Yamaha AN1x's controller knobs for example, it sometimes appears that they used cheap encoders with maybe even just 6 bits of resolution instead of 7 bits, since most of the time you'll see values jumping by a distance of 2 instead of 1 if you slowly turn the knob. In that case, it would of course be senseless to even think about sending these values as 14-bit CCs. If you're looking for a poly aftertouch controller anyway, changes are higher that it will also have 14-bit controllers if it's recent enough, I guess. The Novation SL MkII seems to have both on first glance.