Yes, this is the sort of thing I was wondering about -- it seems as though it's not just about a machine's absolute specs...as it sounds like you're saying that a laptop with the identical hardware of a desktop might still exhibit significantly reduced performance because of hardware/structural/heat-dissipation limitations...and if that's the case, it seems as though there still might be plenty good reasons to go desktop...
I haven't looked at the most recent of laptops but typically they're not of equal spec. They often feature "mobile" counterparts of the desktop series which aren't as powerful.
I was using someone's top of the line i7 consumer laptop from HP a year ago. I thought it was all great until I realized it will shut itself down every 45 minutes due to overheating in very hot and humid weather. It would only run properly when sitting on fans which makes the "laptop" part of it useless.
Remember that there is also the issue of cost. An equivalent desktop will set you back far less than an equivalent laptop.
If you're a power user, the best setup is still a regular desktop tower + a 14" slim(mer) laptop for when you're traveling.

(Sorry, just hacking on ya'. But at first glance the post is funny. We know what you meant).