The last few days I've been reading every professional camera review site I could find online about the One. Basically every one of them said that a higher MP count would have helped with detail in daylight shots. So while MP isn't the only thing that matters it certainly matters. And I found a recent interview online with Jeff Gordon from HTC and he talks about the 'megapixel myth'. It's almost like HTC is trying to sweep the truth under the table, and that is really disingenuous.
At the same time, I'm starting to realize that none of these smartphones, Nokia 1020 aside, can rival a great point and shoot. Even MRU's great photo looks like it was taken with a smartphone in my eyes. So if I personally determine that a smartphone camera has a certain ceiling, then I can potentially justify the M8 as my next purchase.
On a related note, I think the iPhone 6 has so much potential to blow away all these other 2014 flagships with respect to size and design. All these Android offerings are just too big and heavy IMO. I bet the iPhone 6 will be slightly larger than a 5/5S but with a 4.7" screen.
Another thing about MP's. Can't you envision a consumer going to the store and looking at both the S5 and M8 and finding out that the S5 is a 16 MP camera compared to the M8's 4. And that difference could potentially sway them to purchase the S5? Forget what that means in terms of real world usage. You'd be amazed by how many consumers base the quality of a camera on just the MP count.