I know Nev Lapwood and I think he's done a great job with SA. But he's got everybody thinking even legged pop is "proper" and now I've seen it in the CASI manual. And while it might be a safe teaching method it's a technique that was more common off of giant tables.
The best riders I see everyday are popping off their tail on 3s and less and almost always on straight airs. And some of the sickest riders I know pull that technique on pretty big booters.
Both ways work. But it's the raddest feeling and the sickest style to see a guy who gets a freaking rainbow arch off a simple kicker. I can't even stand to hit small or medium size jumps without it.
Erm, I run a totally different snowboard company to SA and Nev, not sure why we're bringing him into this, although I guess me and Nev teach spinning the same way in the same resort town (we're both Canadian instructors so it wouldn't surprise me if we do).
As you said, both ways work, I think the method you're describing is rarely taught anymore because of the way instructing tends to work.
In general, instructors like to teach the most common way that will be easiest to learn and that can easily be applied to the most things. So while your method of ollies works fine on smaller jumps, instructors like teaching the current pop method that will be the most stable and apply to all jumps (small, medium and large jumps).
Your way would work too, but if instructors taught that, then they have to teach them this technique, then the other technique later for bigger jumps, then teach the difference in when you should use it etc. etc. Plus a lot of people tend to struggle with being stable and doing ollies off jumps when they're beginner/intermediate riders just getting into park.
You're right, a lot of good riders ollie off small hits to get more air. It's just slightly more advanced and instructors don't like to teach it early on because it tends to screw people up trying to learn it vs. just teaching pop first.
To give another example, it's kind of like how you can 180 off a jump by rotation and counter rotation (rotating your upper and lower body opposite ways - like how you rotate for a frontside boardslide to regular), and some advanced riders will use that counter rotated 180 to add cool shiftys and other things into their 180, but it's not taught as much to beginners early on because it tends to mess with them if they get used to counter rotating their 180s, then have to change their entire technique up to do 360s and 540s.
So yeah, hope that sheds some light on why you're seeing more people taught pop vs. learning ollies off jumps right away. It's just about instructors preferring teaching the easier to learn, and more useful technique before they get to advanced methods that are more of a special use technique.