Heck, I don't play a lot of XBox and so I still get confused which order the X and Y buttons are in.
I do too, but that's because the buttons have absolutely nothing to distinguish them other than their labels. Heck, I had the same problem with the Playstation shape buttons at first. I've been playing Playstation games for long enough that I'm used to it now, but I remember being seriously confused about which button was triangle, which was square, etc. when I started out.
I just don't see that problem with rear buttons, though. They're ergonomically distinct. First of all there's the obvious distinction between the left and right halves of the controller...hard to get confused about that. But on top of that, the positioning of the buttons is far enough apart vertically that it becomes obvious which is which right away.
Also, I think Valve is counting the clickable touchpads in their 8 buttons-without-taking-thumbs-off-the-touchpads number. Which means there's only two extra rear buttons (one on each side...) compared to what we're used to with triggers on current systems. That doesn't really seem confusing to me. Honestly, I wish there were more rear buttons on current controllers. Why do my thumbs have to do all the world while most of my fingers are doing literally nothing?