That is not true for the new APUs. AMD's new mobile APUs in the 4w to 15w range called Mullins and Beema (evolved from Kabini and based on Jaguar micro core architecture) are based on 28nm chips manufactured by TSMC and are designed to run extremely cool and efficiently.
The problem for AMD is, Haswell is 22nm chip and the coming Broadwell is 14nm chip. There is no way that 28nm can compete with 22nm or 14nm in power efficiency. And Intel is damn good in power-efficient designs.
AMD can compete with a lower price. However, Apple products do not compete on low price, so Apple and AMD are not a good match.
BTW, I like that AMD does its best to compete the giant Intel, and I like AMD as an innovative company.