The only effect I've seen from -webkit-text-size-adjust is that it prevents weird, seemingly random text resizing. It certainly doesn't prevent zoom (on the iPhone) as I can still zoom in when using this.
If you resize the browser in chrome to trigger the media query you set you can see that it stops the text from being resized. I wonder if the mobile version has been updated to avoid this or its zoom is independent?
This was the quote from the post I linked to that seemed to suggest that mobile wouldn't zoom either.
By setting -webkit-text-size-adjust to 100% instead of none Safari keeps the same text size after an orientation change, while still allowing the user to zoom in if they need to. Setting it to 100% also seems to leave user resizing of text alone unlike none.
I've just wrenched my wife's iphone from her steely grip and tested and it does seem that you can still zoom the text on the iphone with the value "none" set.
So it would be safer to apply that media query rule of yours via min-device-width and max-device-width instead of giving it to desktop browsers also.