Since SOX? A perspective I've heard echoed by a few venture firms is that allowing insiders to sell a portion of the shares allows a bit of the pressure to come off and lets them focus on longer term value instead of wanting to rush into a liquidity event. Could be BS, who knows, but it's certainly happening.
A bird in the hand is still worth two in the bush, even if you're pretty sure you can get the two (or four) in the bush later.
Having been involved in a few startups where my equity was eventually valued at nothing, I'd certainly jump at the chance to sell some percentage of a future company I was involved with for real cash money even if I was pretty certain the stock might be worth more later.
