The goal is to provide the some precision that a mouse can, not replicate sticks... If that were the case, they would have just put sticks on the thing.
You can trivially replicate joystick behavior with a touchpad - note how the controller has a raise "home" circle in the middle. This is almost certainly so that it can be used as a joystick, where the input is based on how far from center the thumb is, rather than the thumb's absolute position on the touchpad.
Albeit without any of the tactile value of the tension of an analog stick. [1] Nor an absolute, physically constrained, "max" position: where the stem of an analogue stick is pressed against the edge of its container. [2]
A trackpad seems like it will very easily allow your thumb to drift from a position of sending maximally-distant-from-center input to not registering any input. That's going to be a huge usability problem.
And making assumptions about what a user might have meant should a thumb just happen to slide off the edge of a trackpad is going to be problematic. [3]
[1] What would you call a 360 or dual shock controller with analog sticks that have no tension-to-center anymore? Broken.
[2] Think of how often you feel/hear that little analog stick "clack". Think of how often you're pressing against that physical boundary to ensure maximal-distance input. Each of those moments is an opportunity for a trackpad to present a problem. And those moments are awfully common. It's likely they're more common than not.
[3] did their thumb slide off, or did they raise it? did i slide off on accident or on purpose? etc
I'm guessing that that's what the outer circle is for, right? Your thumb feels the ridge, and that section of the pad is interpreted as maximal-distance input.
I'm not convinced how well that ridge is going to work over the course of, say, an FPS or platformer game session. For a strategy game or lower-pressure situation it's quite likely just fine. But for action games... maybe?
But the lack of tension is going to be a bummer for action games regardless.
We tried that relative-to-an-absolute scheme on our iPhone FPS and it was very confusing. The best scheme was a relative-to-a-relative center where the origin would "follow" the thumb, but then we had a full screen to do that.
The problem with a relative-to-an-absolute scheme (even one with the little raised circle) is you have no idea where the thumb is until you touch the control but then it's too late.
Not saying it can't be done, it's just a little bit tricky.
