On the MBA11, I was slightly imprecise with that statement. I recall that pinch-zooming was bound to Ctrl+ on Firefox. But that is not what pinch-zooming does on MacOS. On MacOS, the zoom level remains unchanged (e.g. 170% for Hacker News) but the window content is smoothly zoomed in and out, without re-rendering the text or images. The zooming is so smooth and responsive that it feels like it's doing fractional percentages. There is almost no input lag from the movement of the fingers.
The Ctrl+ action, on the other hand, changes in discrete steps, (e.g. 100%, 110%, 125%, etc), and there is a noticeable lag caused by the rendering of the window content using the new zoom level. I find the Ctrl+ action to be unusable. (Addendum: On some web pages, I see an image that is too small. So I hit Ctrl+, which causes the image to become smaller. Argh. Pinch-zoom on MacOS causes the image to become bigger, because it doesn't change the zoom-level.)