For those people the same amount of BTC was still in their wallets, providing they could access them (i.e. didn't throw out the hard drive/PC that held them).
This is just sheer negligence - negligence that shouldn't be a burden on the developers part. It is the investors responsibility, not theirs.
If i were an investor in anything, i'd be making more of an effort on my part to at least follow it on a weekly or at least monthly basis, especially in a fast paced and rather volatile market such as crypto's. BTC was also a major exception to the rule - there were no crypto markets then, peoples negligence was somewhat justified. Things are different now.
So is it really so demanding that they at least spend a few hours a night, maybe once or twice a month, to follow their investment and the terms in which they may need to abide by to claim? How is it possibly the fault of the devs if people are so flippant and care free that they just throw money at projects and expect -- no, demand -- some sort of reimbursement of what little efforts they put in?
I do believe it's ultimately the people who participate in these currencies that make them what they are - which is why, to some extent, i'm with you on not keeping it aside as a "development fund".
However, given that too many people just throw money at this project, and not follow it, are they really individuals who can provide something to NEM and it's ecosystem? or have they proven that they're simply in it for a quick buck, their own gains, and washing their hands of it once they're satisfied? At least having some sort of redemption limit, some sort of terms that it requires people to show some vested interest.
In the end, this is what most people will do regardless of the outcome. It's unfortunate you'd feel that way but really, in my perspective; it's your loss.