If they have the volume, which they probably will, more profit. This will allow them to do more R+D and eventually not give a portion of their profits to Intel for the big chips.
Chips are plenty powerful enough to run apps (for the standard consumer). Now the race is to be the most efficient chip, and since that's a fairly new race Apple should have a good chance at it.
Efficiency isn't a new race. What's happening is that the desktop market segment is learning efficiency to meet the demands of the developing performance mobile segment, as traditional mobile is learning performance to also take that segment. That's a race that has been developing in the semico designers for around eight years, give or take, but product has only been available on the store shelf for a year or so.
You have to earn a return on all the additional assets you have by going vertical. The Street will punish you if you just buy companies to make more "profit" but your return on assets decline.
Real reason is probably tweaking designs to their needs in a way that competitors can't access.
Chips are plenty powerful enough to run apps (for the standard consumer). Now the race is to be the most efficient chip, and since that's a fairly new race Apple should have a good chance at it.