Microsoft, Google, and Yahoo all provide a desktop and two monitors (or one 30" one), or did the last time I worked for or interviewed at these companies. They might also provide laptops, but they aren't the primary device for dev work. I seem to recall the same for Amazon, but am not certain.
I actually don't understand this belief that a laptop should be the primary device given the body of research that shows the usefulness of multiple large monitors (unless you're just docking the laptop).
Of course you're "docking" it. Nobody sane hunches over a laptop all day every day.
The advantage to the laptop is you can have your core machine with you everywhere -- home, office, or traveling. But when you're in the two places you spend the most time -- the office or at home -- you plug it into an external monitor, keyboard, and mouse.
I actually don't understand this belief that a laptop should be the primary device given the body of research that shows the usefulness of multiple large monitors (unless you're just docking the laptop).