I have been told by my local tire shop (which has about 40 locations) that the tire tread flexes less as the tread wear depth decreases.
So, yes, new tires wear quicker and those with less tread depth left wear slower. This isn't some mystical formula, just common sense...think about it, they're rubber...
And no, I'm not enough of a fanatic to go out there with a tread wear depth gauge every few thousand miles once the tires are half worn out, I'm taking the shop's word for it. You may consider my opinion worth what you've paid for it.