In my opinion, OmniVision (OVTI) should definitely be on the Top25 fabless list. It had more than $920M revenue for 4 quarters ended in Jan 2012.
Also, when did the old HP Semi group (aka Avago) become a Singapore company? On its own web site, it is happy to state "Avago Technologies Named One of America's Most Trustworthy Companies by Forbes." Does that mean for tax (or tax evasion)reason, it is registered in Singapore, but for business reason, it still likes to claim itself a US company?