I don't quite understand why this article doesn't recommend using <link rel="canonical" href="..."> as described at http://googlewebmastercentral.blogspot.com/2

I don't quite understand why this article doesn't recommend using <link rel="canonical" href="..."> as described at http://googlewebmastercentral.blogspot.com/2009/02/specify-your-canonical.html http://googlewebmastercentral.blogspot.com/2009/02/specify-y... (resp. http://googlewebmastercentral.blogspot.com/2009/12/handling-legitimate-cross-domain.html http://googlewebmastercentral.blogspot.com/2009/12/handling-...) Such an easy solution to this problem.