I think that's the reason, older people are not likely to have either. But if you are under 50 you most likely don't have a landline anymore. Rely on Netflix and a smartphone.
I'm in my mid-30s, only have Netflix since I'm a T-Mobile subscriber, haven't logged on to it since December though. Have a landline since since there's poor cell phone reception where I live, plus I find talking on smartphones uncomfortable. Two years ago I was without a cell phone for almost a week while I sold my Nexus 6P to eBay and was awaiting my Pixel XL to arrive. Awesome week! I forgot how free you are without having that damn digital dog chain around. Most of the time my phone stays in my car or on my desk at work. If I forget my phone at work, no big deal, it will be there in the morning. I feel incredibly lucky to have grown up in the 80s and 90s, being one of the last ones to have a real childhood and to have all of this technology pushed on us and poison us.
If having mobile email and RDP capability wasn't a requirement for work, I don't think I'd even have a smartphone anymore. Might not have a cell phone period.
My aunt and uncle who are in their late 60s don't have cell phones, never have, never will. They don't even allow them in their house. We'll they don't allow use of them. If they see you with one, they'll either tell you to put it away or leave. Their school of thought is if you come over to visit, you visit with them. If you are bored and need something else to entertain you, or are having a conversation with someone else, then you are welcome to leave. And I 100% agree. A couple of my friends would come over and spend most of their time on Facebook or Twitter. After three times of this happening I blocked those sites and a few others on my home network. Again, if I bore you, you are free to leave, but I will not allow that trash in my home.
How many stories are reported every summer of so called parents forgetting about their young kids in a locked car? Or the so called mom that forgot her newborn at the airport a couple of months ago. You know what these people probably didn't forget? Their smartphone.