Is that what determines a flop, though? Siri is definitely known, and added value to the iphone and the apple brand overall. While I use Google Now and think it is superior, I'm not sure if performance would be enough to label Siri as a flop.
Probably the differences are only noticeable for non-native English speakers like me only. It's way too good that it makes me feel Siri is such a failure.
Native speakers might not see a huge difference though.
I am a native English speaker and Siri constantly misunderstands me. Siri has become a punchline and certainly does not have the usual Apple Cool Factor.
Bing on the other hand, not so much.