I respectfully disagree. Let's say Google starts to accept BTC. It'll make the news and all, but so what? People are still going to do business with Google using their credit card, Paypal, Google card, or whatever. What's the incentive for any of Google's customers to switch to BTC instead of some electronic form of fiat? It's almost like if some other company starts up a Paypal competitor and called it SuperPayMeNow. Why would people switch to SuperPayMeNow instead of what they've been using for years? Maybe this new payment system charges less fees to the merchant. Maybe merchants will offer customers a small discount. But I just don't think these small incentives are enough.
I agree with some points, but bitcoin adoption would spread considerably if big companies like those mentioned start accepting it. Maybe not explode but I think it would be the catalyst in a bigger growth over time. People would probably gradually switch over from Paypal if another better system came out and if "SuperPayMeNow" was considerably cheaper to use and was accepted everywhere like Paypal is. If places don't accept something then that is a big barrier to adoption so the more places that accept it the better for everyone and ignites bother interest and growth.