Ian Sommerville went on a tear the other day about IEEE not supporting open access content. I suspect that IEEE uses the revenues it gets from publication subscriptions to subsidize other activities like conferences. I think the open access model for research publications is inevitable, especially in tech-savvy fields like electrical engineering and computer science. When that happens, the IEEE may find itself in the position that the newspapers did when one of their profit centers (classifieds) got disrupted by free online services like Craigslist, making it difficult to fund the cost centers (news reporting).
Mind you, if free journals and fewer subsidized IEEE conferences means that computer science shifts from being conference-oriented to being journal-oriented like the rest of academia, it will probably be a benefit to the CS research community. But IEEE will have to either reinvent itself or go the way of the local newspaper.