Margins on CPUs for tablets and phones are not all that high. Intel enjoys pretty amazing margins on their desktop market, so they aren't missing too much there. They just need to keep ARM away from their bread and butter of profits, which probably can be explained by their current push to keep ARM out.
No, but tablets and smartphones are starting to affect the PC market. Desktops are dying, and laptops are stagnating.
For a lot of people, a smartphone or tablet is sufficient to meet their computing needs. Especially with ability to connect a TV and keyboard, and a number of small ARM based "mini PCs" starting to arrive.