Mixing different 76-keys arranger keyboards (like G-70 and E-60) doesn't make sense (even if they are from same manufacturer and so "alike" as in former example) because they have different features and might be targeted to different parts of market.
Keybed, no matter how important (because this is primary "interface" between player and the instrument), is not the onliest "quality" of 76-keys arranger, and cannot be considered the onliest reason for buying, or not buying it.
Somebody buy 76-key arranger because of the fact that it has 76 keys, but others buys it because of the keybed quality (Roland G-70 for instance), or because included sampler (Korg Pa 1x Pro), or live arrangements (Ketron SD-1), and all these reasons are not the onliest one that made someone made specific purchase decision.
By buying any 76-keys arranger customer gets all the "bells&whistles" but also all negative sides, like size and wight, that might be very important to gigging musician who lugs his instrument to every gig. Even on this forum we can read complaints on size and weight of G-70, and we can be quite sure that keybed is not the reason (at least) for heavy weight.
I am (still) not a keyboard player, but, from what I have seen and read until now, 61 keys are quite enough for an "average" one-man-band player.
Advantage of having 76 keys is having one more split point and additional sound without touching control buttons, and/or wider key-span for playing more demanding (piano) music pieces. So, if I'm right, only "advantage users" who do want to perform something more then one-man-band show needs 76-keys.
So it is quite understanding that there is more demand for 61-keys, then for 76-keys keyboards (there are more amateurs then professionals). The results of the pool on this forum might just indicate that majority of the members are professionals or advantage users.
But, although the number of potential buyers of 76-keys arrangers is smaller then the number of buyers o6 61-keys keyboards, it is still profitable market.
And not only that, but also all the users who wants to have the TOTL arranger keyboard from Korg, Roland, or Ketron, will end up buying 76-keys arranger keyboard weather they need it, or not.