For at least a little while I've had a theory, in fact a "belief," that there's still a weight shift to the right in an S&T swing. My reasoning was that your chest is in front of your spine, your arms are in front of your spine, your belly, etc.
So to test this I got two scales and Dave, James, and myself set up on them. We got into a setup which we were happy to see was between about 55L/45R and 50/50 for all of us. We made a backswing and stopped at the top. The two who weren't making the swing checked the scales (which measure weight, and not what the guy swinging would perceive as "pressure" - I'll get to this later).
Turns out that at P4 the weight was anywhere from 55L/45R to 45L/55R. Very little movement was necessary to tip the scales the other way - from the weight staying forward to the weight actually moving a little backwards.
I had guessed that a stock weight shift with a "perfect" backswing might get to 45L/55R, and while that's still "plausible" using the Mythbusters method of rating things, in reality the range of motion required was so small that while static weight does get to 45L/55R, determining WHEN it gets there becomes a matter of precisely defining the "top of the backswing." If it's when the club changes direction in a dynamic player, the hips may have already started going forward and you can get numbers from 45L/55R to 55L/45R. And these differences are very difficult to see on a camera.
So before I follow up on the "pressure" comment from above, a quick comment... There's still a weight shift in S&T. If you get 90% of your weight on your front foot just after impact or at impact, the only way for there not to be a weight shift would require you to have 90% of your weight forward at the top of your backswing. Any amount smaller than that is, by definition, a weight shift. Weight is still moving to the front foot throughout the downswing, even if you really had some goofy backswing we wouldn't teach you that put 80% of your weight on the left side at the top. In reality, the weight shift is from roughly 45-55% left to 90% left (95% or so farther into the follow-through) depending on when you define the top of the backswing (P4).
Now, to the idea of pressure. The simple fact of the matter is that when you're not moving, pressure into the ground is the same as weight. If you bend your knees quickly you decrease pressure as your body drops, and if you jump, you apply more pressure to the ground than you weigh (that's how you get off the ground - you're overcoming your weight - gravity - with your muscles).
Also, this: stand up straight. Sense how much "pressure" your leg muscles feel. Simply put you can stand relatively upright for hours and hours and hours. Now bend your knees about 45 degrees - how much pressure do you feel now? You've not gained weight, but you feel a lot more tension in your muscles.
In reality, the pressure - through the soles of your feet - is the same in both instances, but I think people overdo the "weight shift right" because if your right knee decreases its flex/straightens even a little (and if your hips turn, your right knee is virtually guaranteed to decrease its flex), it will feel less tension. Your body will tell you there's less pressure there even though there's more, so you'll shift even more weight over there to really feel the "tension" which you feel as pressure.
If you ask people making a centered shoulder turn how much pressure they feel in their left leg and foot, they'll often say it feels like 80% of their weight is there. It's not - but because of the differences in how the legs are flexed, it might feel like that to them. Our bodies are not great (some are better than others!) at feeling "pressure" in the soles of our feet - we'll often mix in muscle tension and stretching and things like that.
P.S. When our legs are straight the muscles don't work as hard because the bones support most of the weight. When our legs are flexed, our muscles do virtually all of the work.