The ratings agencies were pricing in the risk that Apple lobbyists would not be able to bribe the US Congress to allow overseas profits to be returned tax-free.
To be fair, not only Apple has been lobbying for a tax holiday, also parties like Google and Cisco. Both those companies are sitting on cash in tax havens, but I haven’t seen the market act bearish over it.
http://www.bloomberg.com/news/2011-09-29/google-joins-apple-...