I think the point is that the numpad isn't free if you use the mouse with the right hand. It takes space on your desk, between the actual keyboard and the mouse. This stresses the joints a bit more. You either have to grab the mouse way out to the right, or type with your hands to the left.
So if you only use the numpad "1% of your day", I'd say there are reasonable reasons, outside of vanity, for preferring a keyboard without the numpad.
Sure, if you mainly use the mouse and the keyboard single-handedly (say, like a gamer would), the numpad probably doesn't bother you.
I'm not particularly into "vanity shots" of my desk, but I absolutely curse the full-size keyboard whenever I have to use one.