Noted Apple (AAPL -2.19%) analyst Neil Cybart recently tweeted the following: 

Cybart didn't provide a link to a source, although I wouldn't be surprised if this conclusion was a result of proprietary research. 

Apple's iPhone X.

Image source: Apple.

At any rate, Cybart is well known and widely respected for his Apple analysis, so I'm willing to accept this statement as true. 

Cybart later went on to offer his opinion as to why the iPhone 8 Plus is outselling the iPhone 8 in a subsequent tweet: 

Although I'd certainly agree with Cybart that user desires for greater screen real estate, coupled with the superior camera features (the iPhone 8 Plus has a dual-lens camera subsystem that supports Portrait Mode, Portrait Lighting, and optical zoom) is helping to drive mix from the iPhone 8 to the iPhone 8 Plus, I think there's another factor at play: iPhone X. 

4.7-inch iPhone buyers going with the X

I suspect that during the iPhone 7-series product cycle, there were many iPhone 7 buyers who would've been more than willing to pay extra for the improved camera features in the iPhone 7 Plus, but simply thought the phone was simply too large.

Those buyers, who would've simply purchased the iPhone 8 during this product cycle, now have a better option: iPhone X. 

iPhone X, due to its all-screen design, offers a large screen with much greater screen real-estate than the iPhone 8 does, while also offering all of the camera improvements found in the iPhone 8 Plus -- along with some extra ones. 

Additionally, I don't think this phenomenon is limited to smartphone camera enthusiasts, either. I expect that there's a sizable number of individuals who simply want to buy the best iPhone available in any given year as long as it's not unwieldy. 

Those buyers would've been forced to go with the iPhone 8 had the iPhone X not been offered this year, but since the iPhone X is an option, those potential customers are going to opt for it. 

Now, this isn't to say that all potential iPhone customers that are waiting on the iPhone X would've bought the iPhone 8; there will certainly be those buyers that would've opted for the iPhone 8 Plus absent the iPhone X that will buy the iPhone X. 

What I'd be willing to bet on, though, is that a larger proportion of would-be iPhone 8 buyers are waiting for the iPhone X than would-be iPhone 8 Plus buyers. 

Combine the two, and iPhone 8 Plus outsells iPhone 8

The combination of the factors that Cybart mentions (which, in effect, boil down to the iPhone 8 Plus being the better phone) as well as what I believe to be would-be iPhone 8 buyers holding out for the iPhone X seems to be leading to the iPhone 8 Plus outselling the iPhone 8. 

Such an upward shift in product mix is ultimately a positive for Apple, as it could mean significant iPhone average selling price growth -- and thus an increase in iPhone revenue -- year over year during the current product cycle. 

Moreover, this seems to lend further credibility to the notion that iPhone customers are willing to pay more to get more. 

As Apple continues to amass evidence in support of that notion, it can be more aggressive in bringing new technologies, features, and ultimately user experiences to its iPhones.