Yep. This convention also enables the cancellation of a click, which can be useful if you realise your error mid-click.

Another piece of software egregious for violating this UI convention is Adobe Reader. I remember upgrading to, IIRC v9? and finding that all buttons in it had been changed to actuate on mouse-down, and wondering what the christ the developers were thinking. Perhaps they thought it made their software seem more "responsive".