So I finally got around to reading this topic and I've got to throw in my $0.02.
First, there are two kinds of tip lead. Good and bad--or possibly more accurately, natural and unnatural. Bad tip lead occurs if and only if the heel of the inside foot is forward of the hips. The reason this is bad is because it limits your ability to shift your weight to the inside foot in order to make a transition (or make a recovery move if you are skiing two-footed). If the ski is forward, you will either not be able to shift your weight at all, or you will be able to do so, but only at the expense of being in the back seat. In either case, you will not be able to make an effective transition. This is the only level of tip lead that is counter productive.
When skiing with equal weight distribution on both skis, reducing tip lead beyond what you get naturally (by pulling the inside ski back) can be beneficial in that at will allow more uniform flexing, more parallel shins, and more uniform edge angles. However, not all situations recommend themselves to skiing this way; it should be a choice, not a dogma.
So what is "good" tip lead? Good tip lead occurs naturally as a result of countering. Countering is necessary for proper hip angulation. Hip angulation is necessary to put weight on the outside ski (more angulation == more weight). To acheive any kind of an edge angle, we have to inclinate--that is position our body to oppose the centrifugal force stacked against us in the turn. However, leaning directly into the turn does not allow us to put weight on the outside ski. To do that we have to shift our torso back towards the outside of the turn. One way to do this is to bend outward at the hips, but the problem is we don't get very much range of motion this way. A better approach is to open the hips towards the outside of the turn (counter). This enables us to bend in what is now a forward direction, which gives us the full range of motion to push our torso out over our skis. Additionally, this motion stacks our body such that the femur of the outside leg takes all of the weight. IOW it puts the weight where we are strongest and most able to to take it.
Now the motion of opening our hips is what creates good tip-lead. This is what you are seeing in the world-cup montages. If you stand with your feet facing forward, shoulder-width, and swivel your hips to the right, you will notice that your left knee collapses, and your right leg straightens. Your left foot wants to slide forward, but it can't because you are standing on it. On snow, however, it will slide forward. The key, however, is that it will remain underneath your hip--keeping you in balance.
A while back there was a thread about pushing the inside foot forward to start a turn. At the time I suggested that motion was an effect rather than a cause in a good turn. I'm more convinced now than ever that my intuition was correct. The problem with thinking of pushing your foot forward, is that motion is not self-limiting. If you slide your foot forward, you can keep going until the back cuff of your boot stops you (or if you want to pick up your ski, you can go even further). Regardless, pushing your foot forward moves it forward of your hips and out of balance. However, if you start to counter with a hip rotation, your foot will clear forward, but the motion is naturally self-limiting and it will remain under your hip where it belongs. It may feel as if you are pushing your leg forward, but the key is that the hips control everything.
My guess is that the "push your inside leg forward" advice is causing people to develop bad tip lead because it automatically puts them out of balance. The only recovery is to pull your foot back under your hip where it belongs--but then if you used your hips to begin with, you would never have to do this.
As for the notion that you get tip-lead when you steer (or "pivot") that is certainly true, but so what? Steering is a valid way of initiating a turn and must happen in order to execute a turn inside of the ski's turning radius. Most race turns happen that way--steer to an angle that will allow you to intercept the arc at the point in which you can finish your turn where you need to be. Regardless, the tip lead you get from steering is the same you get from countering--if you are steering with your femur, your feet don't move out from under your hips, so there is no problem.