I think it was a pure profitability thing. I chucked some serious volts through my 680's with the ArtMoney hack and they absolutely flew. If I was braver, I would have kept 1.45V running through for gaming and running a 1400Mhz clock and I can see those clocks that I had matching the 780 (fps wise) if the rumours are true.
At the time, I believed it to be on saving RMA's and keeping max profits (no voltage tweaking = less returns from over volting) but not so sure now.
All speculation.
I think this was the initial feeling when the 680's launched, over volting and thus big clocks may snatch sales from the next top line as we know a stock titan = roughly 7970 @ ~1300mhz, a 680 at a similar speed may well be clipping titans heels as well. Though the RMA factor also comes into it, I'd love to see returns figures vs. older generation (or even vs 7970 with unlocked voltages) to see if it has actually done anything to reduce the number of faulty cards.
Its a shame but its a direction Nvidia seem to be taking. Just hope AMD don't take a similar stance as it could potentially destroy absolute top end cards such as the Lightning, Classy, SOC etc...that are geared towards over volting.