In this instance, to my knowledge, Apple isn't using shell companies. It has iTunes set up in Luxembourg, but that's a very real company. And each country has it's own Apple subsidiary which again are real companies in their own right.
I'd say that it's hardly tax avoidance, since they pay their taxes in the countries where the revenue is generated. No one in their right mind would give up 35% of their wealth simply to move it to a different country, and nor should they.
Please go read the links. This is not about the sales happening in countries outside of the US. This is about the billions of dollars inprofits Apple, Microsoft, Google and others would otherwise be making on their US sales being shifted around to low-tax havens using clever internal licensing agreements. For example, see http://www.bloomberg.com/news/2010-10-21/google-2-4-rate-sho...
I'd say that it's hardly tax avoidance, since they pay their taxes in the countries where the revenue is generated. No one in their right mind would give up 35% of their wealth simply to move it to a different country, and nor should they.