Ian Johnson said recently on an episode of Xtreme 4x4 something to the extent of, "You can get a rental car through just about any trail with a winch". That sorta validates and invalidates the whole winch vs. lockers thing.
It validates it because once your really stuck, a winch is usually the only thing that will get you out. I've been stuck with both my ARBs locked more than once and had to rely on the winch to get me out. If you off road alone, a winch is an absolute necessity IMO - over lockers, lift, tires, or anything else. I personally don't go on hard trails without a buddy (and most of my wheelin buddies have winches) so I haven't felt the need to buy one yet. But, I don't like having to bother my friends to get winched out unless I absolutely have to. That's why I got lockers, because most of the time I can make it through by myself.
Ian's statement also kinda invalidates the winch vs. locker thing to because putting a winch on a rental car might make it possible to complete the Rubicon, but it doesn't make the rental car a capable off roader. An off roader is supposed to make it through under it's own power.
Ross, I hear what you're saying about a locker causing you to push it harder and farther, but that's true for regular 4x4 and even 2wd. Lots of people make it over that first obstacle and they're so impressed with their truck that they think they can do anything after that so they push it farther and end up getting stuck. But you can't blame that on having lockers, or 4wd, ATRAC or anything else.. The driver not knowing his or his truck's abilities and not knowing the trail is the problem. No one should be pushing any limits by themselves, especially on a trail they aren't familiar with. But if they do, I agree.. they better have a winch!