Not being able to sneak attack beyond 30' DOES make a lot of sense, if you look at it in the way the designers envisioned: you need to see clearly which part of the enemy's anatomy you're attacking etc.
However, what about sniping at unaware enemies? Why is the Assassin's Death Attack, which takes a massive 3 rounds to set up, AND an unaware target, limited to 30'? The way I understand it, a good archer can put his arrows in a stationary or slowly moving target wherever he wants to, and at much greater range than a measly 9 meters.
I could understand if they'd put in some restrictions, like "You have to aim carefully if you want to use sneak attack at longer range. This takes a move/standard/full round action." Something like that. Or maybe just lower sneak attack dice by one for every 30' of range between you and the target. But just flat-out forbidding it always seemed rather strange to me. A precision-focused archer shouldn't be limited this way IMO. That's why I think the rule is stupid.