Pocket, a service that lets people save stories and videos to read/watch later, published data on how user habits are changing thanks to the bigger screens on the iPhone 6.The iPhone 6 has a 4.7-inch screen, and the iPhone 6 Plus has a 5.5-inch screen. The iPhone 5S has a 4-inch screen. The iPad Air has a 9.7-inch screen, and the iPad Mini has a 7.9-inch screen.As you can see in this chart, iPhone 5S users spent just under half of their time reading on the iPad versus the iPhone. But, once they got an iPhone 6, they only spent 28% of their time on the iPad. When they got an iPhone 6 Plus that dropped to just 20% of the time on the iPad.If this trend holds for other apps and services, it spells doom for the iPad. If someone only needs an iPad 20% of the time, Apple is not going to sell very many iPads.People who want to sound smart say that this doesn't matter for Apple because the iPhone 6 and 6 Plus make more money for Apple. The iPhone sells for ~$650. The iPad's average selling price last quarter was $431.66. The iPhone is much more profitable.But, in an ideal world for Apple, it's selling a $650 iPhone,anda $431 iPad,anda $1,200 Mac, and a $400 Apple Watch,and, what the heck, why not toss in a $99 Apple TV, too.Instead, it looks like Apple will be selling a $650 iPhone every 2-3 years, a Mac every 5-8 years, and maybe an iPad every 4 years, or maybe not, if people are buying the iPhone 6 Plus. As for the Apple Watch, who knows.For Apple, and Apple investors, this is fine. The iPhone is really all that matters for the company. And, Apple has to be willing to let its products compete with each other.So, the smart people that say this doesn't matter are right. Apple shouldn't care if the iPad is killed by the iPhone. It's much better than watching the iPad get killed by a Samsung phone.Join the conversation about this story Click here to read full news..