I think the terms weighted, semi-weighted, synth weighted etc., are VERY loosely thrown around. And quite often engender an argument that bears no basis in fact. I am pretty sure that the 'weight' to press a key down between a PSR and an FSX varies so little, it would be hard to tell with a blindfold...
There are four or five factors in the 'feel' of a key. Yes, the mass of the key itself (highest in real piano keys), the strength of the spring, the tightness of the hinge (how much play there is) and the feel of the key as it comes to the end of its travel. And maybe the speed of return of the key to its resting state.
While some think weight alone is the factor they can perceive when playing, to be honest, for me, I think the spring rate and the 'stop' are very discernible, but the accuracy of the hinge, its tightness (lack of play) is what I tend to feel the most when I'm judging 'quality'.
In this regard, the sort of 'wobbly' feel from the PSR's is what puts me off the most. Play a real piano, a B3, any decent synth, and that 'wobble' is almost entirely absent. There's a LOT more going on than simple weight...
But Ian... I'm pretty sure the action from my G70, which was pretty heavy just by itself, would mean a heavier case to support it, and then the BK's weight balloons. Which given how aging and weak the arranger playing demographic appears to be (strange how the aging WS playing demographic seems much stronger!), would seem to be the kiss of death to sales. Not to mention, the G70's action, being longer, means a bigger case there too.
I think the thing which peeves me most about Yamaha's decision to remain with the sub-par PSR action is the decision to put a MUCH better one in WS's costing MUCH less. Yes, obviously, you don't necessarily get the TOTL action in the MOTL keyboard. But, OTOH, you shouldn't really put the BOTL action in the MOTL either!
It's a question of respect... Do Yamaha consider their PSR customers either incapable of needing as good an action action than their WS playing brothers do, or do they consider them so gullible that tossing them this awful apology of an action won't be noticed? Or do they simply rely on the rabid defensiveness of Yamaha users to refuse to make any honest criticism of their purchase to protect them from any comparison when making this decision?
I am convinced that if Yamaha PSR users actually made a fuss, and demanded an action the equivalent of similar priced Yamaha WS's, it would be on next year's model. But keep telling the world how HAPPY you are being shafted like this, what is Yamaha's incentive..?