A big downside to the iPad is slow text input. Many people love their laptops because they can quickly communicate with people.
Citation needed? What do you find buggier about iPads than other iOS devices, and what makes them harder to develop for?
In addition, Apple has it's own "private" API's that app developers aren't allowed to use which makes development more complicated than it has to be.
Finally, iPad's have way more screen size than iPhones. Little things that you might get away with on a 5 inch screen suddenly look really bad when blow up to 10 inches.
It's really hard to say how Android tablets are doing because the market for them is so diverse.
So many people that own one don't replace it until the battery starts dying.