These are more or less the same reasons I pointed out in a post from three years ago about desktops versus laptops: http://jseliger.com/2008/12/26/computer-post-desktop-or-lapt... , and, as people observed then, some of them can be overcome: external peripherals for ergonomics, larger screens, and extra storage.

The real question is whether you a) can or want to afford a laptop, which still tend to be relatively more expensive than desktops and b) whether you're actually mobile enough to bother. In my case, I have a great chair, a sweet desk, two large monitors, and a room of my own; this means I tend to do my best work there.

(Note: I also left this comment on pcmag.com).