Even if you buy the top of the line laptop - it doesn't have much room to upgrade. Graphics cards, ram, hard drive, screens size, durability are just some of the reasons I would go with a desktop. Not to mention even if a motherboard on the desktop dies, you can replace it with endless possibilities and many different options whereas a laptop is way more limited.
laptop vs desktops only wins if you need the mobility or the price of a cheap laptop (for example a $300 laptop is cheaper than a desktop because the screen is included in the laptop)