True, but let's assign a value to the difference in price. When you really get down to it there is nothing a desktop can do that a technologically current laptop can't do. So what kind of value would you put in the fact that you have a computer that takes up less current, easier to transport, i.e. no extra expense for "special luggage", and mobility to work at the beach if you really wanted to.
So, according to Dell the kind of system that I would purchase currently runs about US$950 for a desktop and about US$1300 for a laptop. That's a difference of about US$350.
In the big scheme of things you will need to reach down deep inside you and see if the US$350 premium you are paying for the laptop is worth it. That unfortunately is an individual matter and not everybody will have the same answer. Personally for me the value of my time, mobility, and peace of mind is worth paying the premium. I can purchase for an extra US$100 a solar cell that will let me work on the laptop while it's battery recharges. The amount of business I can conduct will pay for this extra portability and like I stated previously, I can work at the beach if I wanted to.
As you can see, value is purely subjective and is something you learn in Business 101. Who wants to be tied down to a desk when you don't have to? Why not get out and enjoy your surroundings while your making a little extra greenbacks? Why purchase a desktop when a laptop is better?