PC makers have to find a way to condense everything and jam it into a smaller box thats attractive. You have a high end machine like the new Mac Pro, and it looks good, performs insanely and is tiny compared to machines with similar specs. Now, thats something for the professional crowd, but there can be a market for budget PCs that look good. But they have to be affordable and offer the kind of storage that youre not gonna get in a tablet (1TB SSDs, which could get pricey)
I know that I'd never stop using a desktop because I just need to be able to create shyt, type on a physical keyboard and have access to the internals (upgrade RAM, hard drive) and really run the machine into the ground. The iPad and other tablets are cool and easy to pick up and take places, but you cant create shyt on them
on the other hand, you have tons of offices that get these cheapo Dell desktops that they hold onto for like 5-10 years and let their employees abuse them because the machines run Windows and wont cost shyt to fix because they get tossed out and replaced if they break down. A company like Dell or HP eats well off of these bulk sales. Its like a car company selling thousands of cars a month in fleet sales to rental car places like Hertz and Avis.