Canon doesn't have to answer the D4s. It needs to answer the D800(e).
No, they really don't. The 5DIII was the answer, and it has outsold the D800 and far outsold the D800E.
I still think it's possible we'll see a high MP sensor from Canon in the future, not as an 'answer' but rather to capture a part of the market they feel may be untapped. But we'll only see that if Canon feels there's enough of a market for it. I wonder if the D800 sales might be pointing them in another direction...
This is a sensible, yet very stupid, way to look at it. Fans of music artists also waste time on caring about the sales of their own favorite artists. In the end though, all that should be irrelevant to the fans. It doesn't matter if plenty of others bump the same music. Bad sales might actually force something better out the next time.
Canon's sales don't really matter to me. Or actually... Had the 5D3 flopped, Canon would most likely work hard to make improvements and maybe they'd even unlock some of the features that have been artificially hidden to justify the 1DX price tag.
From a sales point of view you can say that they don't have to do S___ now, but instead of viewing the whole situation as a competition agains Nikon, there are other aspects. Besides, they need to beat the crap out of the 5D3 with the upcoming replacement to get money from the 5D3 purchasers again.
The bottom line is though that I don't care how well Canon does on the markets. Nikon can outsell Canon and I just don't care. For me the thing that matters here is the equipment I can afford to use. Surely it's heavily linked to the markets, but that's none of my business.