hey, at first, TSMC is a company in Taiwan. So as their main factory.
And the labor cost is not really a big issue in semiconductor fab. Yield and other issues are more important to them.
Intel made good margin on Atom (http://www.electronicsweekly.com/blogs/david-manners-semiconductor-blog/2009/02/intel-to-out-source-atom.html#comment-1439714). Some people think intel is not good at make low power product. Some others think intel want TSMC to help the industry adopt Atom as part of their design.