Riley Crosby wrote: i can't imagine not pushing the pole up with my left arm. i picture myself running down the runway and planting the pole, and not pushing with my left arm and the pole not bending enough to get me to a safe landing spot in the pit. it seems like the pole would bend a little bit, but not nearly enough before it unbent. i just dont get it.
Yes, I can see how it sounds counter-intuitive. You have to try this with a very light pole at first, then work your way up to heavier poles as your technique improves, and as you gain confidence that the pole will bend without any bottom arm pressure. And you need a coach to walk you thru it ... a coach that understands and believes in the Petrov model. Trust me - it will bend!
I encourage you to continue to read and watch - as you're doing. The more information you understand, the better you'll be able to apply it to your technique.
But if you're really serious about pole vaulting, and you want to jump as high as you possibly can, maybe what you need - in addition to educating yourself - is to find a coach that teaches the Petrov model. Maybe there's no one locally that can help you. (Fill out your PVP profile, so we know where you live.) But if there's ever an Alan Launder BTB2 or Rick Baggett camp in your area, you should seriously consider attending. There's also good camps by other reknowned coaches, but beware of any that teach "big bottom arm" technique. (No camps OPENLY promote "big bottom arm" so you have to do some homework on the coaches' PV models to find this out.)
Your observations of Stevenson and Walker are correct. They do more of a "drive vault", aka "American style", and apply significant bottom arm pressure. However, as Walker has progressed over the past few years, I think that he's trying to become more and more of a Petrov or "swing" vaulter - like Hooker and Lukyanenko. It's just that old habits die hard, and you can't change your technique overnight.
In their defense, tho, I will say that these 2 vaulters are superb athletes, and even tho their bottom arm pressure slows down their swing, their swings are still quite "phenomenal" compared to HS or college vaulters. They have adapted quite well to catching up to the pole (i.e. inverting and shooting before the pole fully recoils). Most mere mortals - especially young HS and college vaulters, simply don't have the athleticism to replicate the technique of Walker or Stevenson. You need super strength and super speed.
One could argue that the same might be true of all the other 6.00 vaulters - like Bubka - that followed the Petrov model. But I think that's exactly the point ... if you learn the Petrov model at an early age, you can progress with a "natural swing", so you don't need amazing strength or speed to invert ... it happens as a natural consequence of your swing. e.g. Hooker.
Now, how does this all relate to how the pole bends "naturally"? Well Riley, this has been mentioned elsewhere several times, but I'll mention it again here for your benefit ...
The pole is going to bend whether you press or not. It's relative to the amount of momentum that you've built up in your run and takeoff. The amount of additional bend that you give it by pressing is very, very small.
I'm not even going to quibble here between "no push", "slight push", or "slight pressure". None of these are "big bottom arm", so let's not even quibble about the subtleties of those differences (for now). Just try to understand where most of the force comes from. It comes from your run and jump.
Now, understand that even tho the bottom arm puts an INSIGNIFANCT amount of additional energy into the pole, it TAKES AWAY a SIGNIFICANT amount of "natural swing". Thus, your swing slows down, preventing you from swinging "naturally" to an inverted position, thus preventing you from shooting straight up EARLY ENOUGH (in unison with the recoil of the pole).
So what must a vaulter do if he finds himself in that predicament? Well, he needs to quickly tuck his legs in, rock-back into a "ball" (or cowboy position, or pike - like Walker), PAUSE while the pole rolls to vertical (towards the pit), then shoot up off the top of the pole. That's a lot harder to do - and a lot less energy-efficient - than just swinging naturally.
In Stevenson' 6.00 at Modesto (and in the 2004 Olympics), he's gutsy, gripping at ~5.10 (~16-9) to his pinky. This is a ~1.10 (~44 inch) pushoff, which sounds like a lot, but is actually average compared to other 6.00 vaulters (See:
http://www.polevaultpower.com/6mclub.php ). Really, Stevenson vaults high because he has a fast run, so he can grip high. His technique is NOT what gets him that high!
Enough about all that.
Riley, find a coach or camp that teaches the Petrov model, and you will walk thru the proper progression of getting the hang of bending the pole THRU THE TOP HAND, rather than thru the bottom hand. It's only thru this practical experience (self-discovery) that you'll finally realize that the pole will bend "naturally". Then you're on your way ... upwards! The sky's the limit!
Kirk
Stevenson and Walker may... But does Tim Mack? 
(But just because it is difficult to imagine does not mean that it's not true...)