If you're interested in ETFs then you have to be interested in Apple.

As the world's largest company, Apple is in many plain vanilla ETFs. With many of the major factors - like momentum, value and quality - Apple is in many smart beta ETFs. As a multi-industry company, it is in many sector ETFs. If only because it is in so many of them, Apple matters to ETFs.

If Apple matters to ETFs so does its new iPhoneX. It is too early to know for sure. But this far out, it is a safe bet that the iPhoneX will be good for ETFs.

Why?

Let's revisit the economics textbooks and recall what price elasticity of demand is.

"Price elasticity of demand" is an ugly phrase but it is important because it explains why the iPhoneX will work for ETFs. The idea goes like this.

Some things people will pay anything for; other things they won't. I may hate rising energy prices but Canberra's winters are cold. So I'll keep paying for heating despite rising costs. In other words, my demand is inelastic. But for computer games I am less set in my ways. If they rise in price I simply won't buy them. My demand for computer games is elastic.

In amongst the brouhaha surrounding the iPhone new features - facial recognition, new cameras and the like - fans also managed to notice the $1,000 price tag (roughly $1,600 in Australia, well above the exchange rate).

Not only was the price noted, it was abjectly ridiculed. With some justice.

The median wage in the US is $865 a week, according to the Bureau of Labor Statistics. The average American spends just $550 a month on food. A very similar phone from Samsung, the Galaxy S8, costs $700—30 percent less than the iPhoneX.

The $1,000 price tag means Apple expects buyers to spend nearly two months' worth of food and more than a week's pay on a new phone. That's a lot of money. All the more so considering that most iPhoneX customers already own a phone.

How do they get away with this? And what does it have to do with ETFs?

According to research published in 2017 by consultancy Brand Keys, Apple commands more brand loyalty than any other company across four major industries: music, tablets, computers and phones.

And customer loyalty is a powerful thing. With high customer loyalty, as Apple understands full well, comes low price elasticity of demand. It allows Apple to charge $1,000 for a phone and watch as customers line up to buy it.

Which brings us back to ETFs.

Apple's share price has been a rollercoaster in recent months. It rose when the iPhoneX was announced, sank when there was suggestion of delays, rose again when potential delays were dismissed, then sank again when the product underwhelmed at launch.

But these short-term fluctuations miss the bigger picture. The bigger picture is that Apple has a new phone that's expensive, price inelastic and, like all of Apple's products, comes with mouth-watering profit margins. (Gross profit margins on Apple products are almost 40 percent, compared with the 28 percent profit margin on Microsoft products).

This has obvious implications for ETFs with Apple in them, all of which are good. If the iPhoneX sells - which, if history is anything to go by, it will - then profits will go up. If profits go up, stocks tend to do well too.

Markets might jitter for now, but they'll settle. As sales results come in for the iPhoneX expect Apple's stock prices - and the many ETFs with Apple in them - to make out just fine.