Desktops of course are more upgradable, more powerful, except a lot of people are willing to sacrifice the power of desktops for the portability of a laptop. Today actually, you definitely can buy a laptop that is way more powerful than a desktop, look at the new acer predator. So overall, neither win, and it depends on what you want, part power and upgradability, or portability, and less power draw.
Yes, desktops are better than laptops because what they lose in portability, they make up for in power and cost. To buy a desktop that is the same power as an equivalent laptop is quite cheaper, and to build a desktop that is more powerful than that same laptop may only cost the price of that laptop.
Well, not forever, necessarily. But laptops come prebuilt, prewired, and once it's dead, it's dead. A desktop can be constantly upgraded, revised, repaired, renewed. Also a desktop computer will always be the more powerful and customizable system. It's a no-brainer, really. Laptops are expensive conveniences for students and workers who travel.
Even, lower power (15W) laptop CPU(s) deliver comparable work experience with desktop computers. Thanks to Turbo Boost, laptop CPU is able to handle occasional power intensive tasks with same speed as desktop. Laptop, including internal screen, consumes less energy than desktop alone. Laptop's price is little bit higher for same performance, but laptop also comes with screen, keyboard, touchpad,... And all of it is packed in compact form factor,... So, laptops are great for work!
Desktops are not necessarily "better" than laptops, because it really depends on the computer's specs. Also whether something is "better" is totally based on opinion. There are laptops that run smoother than desktops, but that does not mean laptops are better. Generally, if you are buying a computer with the same model year from the same company, the desktop will be better. However, I would much rather have an Alienware or a Razor laptop over a Dell Inspiron desktop.