Ah but the beauty is the space / power saved, less constant heat output and you can take it with you if you want to. Mine sits on my desk more often than not these days but it's very useful for these reasons. I did used to use Shuttle XPC's but would still rather have a decent laptop.
Where I work, desktop replacement laptops are on a dramatic rise compared to traditional laptops, even for CAD.
Tis a good point I suppose. Thing is I'd be willing to TRY running a laptop for a while at home but... hmm... my PC at work is due for a major refresh next year and maybe I'd consider taking the laptop route if only as an experiment for how I use computers at home.