Don't take this the wrong way, but a laptop can still suit your needs just like a desktop. For various reasons, I have an 27" iMac and a 15" MBP, and from work, a MBA, full loaded, with a 27" Monitor. Obviously, an iPad 2 as well. So, I've used numerous configurations. Having the portability of a laptop with the "ergonomics of a desktop". I use a normal keyboard and mouse. While you would work from the one on the laptop, it wouldn't make much sense, imo.
Not trying to say you are wrong, just something to consider. As someone who very much enjoys desktops, the laptop + external monitor setup is quite enjoyable.
The main advantages of a desktop over a laptop for me are that the desktop has far more storage and PCI expandability, is suitable for gaming, and since I don't need to work in multiple locations, I see no benefit in being able to disconnect my CPU and use it elsewhere. This frees up precious desktop surface space as the CPU is under the desk, and I don't have to deal with an extra monitor at a weird height and uselessly small size in relation to my main screen, or closing the clamshell to sleep, but then waking it up with external inputs and using it with the lid closed, which is very harmful due to improper ventilation, and I don't want to have to disconnect a bunch of cables when I want to go mobile, or reconnect them each time I want to use my workstation. There are a million small inconveniences to using a laptop as a component to a workstation, to the point that I'd simply rather not deal with it. Plus, desktops are cheaper; I can assemble a nice gaming rig/media workstation desktop plus buy an iPad for the same cost as a nice laptop.
Off topic, but I never thought I'd see someone on HN refer to the desktop tower as "the CPU". That's what Grandma does when she points to the LCD monitor and says "the computer".
Not trying to say you are wrong, just something to consider. As someone who very much enjoys desktops, the laptop + external monitor setup is quite enjoyable.