In particular, I'm thinking that I (a person of reasonable technical skill) would love to help them out by changing the designed-to-be-swapped screen on the phone they dropped instead of them paying someone else to conduct surgery on it.
I have changed the battery on two iPhones on my own, and replaced one screen on my own. I've also once had one of those little shops do it, quickly and cheaply. I only did it on my own because I wanted to see how difficult it was. The savings in money and extra time was completely wasted other than for the entertainment value of changing it.
The slice of people who get entertainment value out of changing their screens, yet does not have the skills to do it on a current iPhone, must be quite small. Surely less than 10% of the population, for a "feature" that has easy alternatives of paying somebody $20-$30.
Those are two very different topics. Sure, cars don't advertise their ability to be maintained without special tools. But I also know a lot of people who do in fact want to change the oil in their own car (because it's not hard, and much cheaper once you have the tools).
If changing the screen of a phone were as simple as changing the oil in a Honda is, then none of this conversation would have to happen.
Big bonus points for making spare parts available without all the BS strings attached that apple currently has.
I see a lot of issues here personally.
Even if the majority of people are unable to do these part-replacements themselves, it is still a massive improvement to make them easy to perform. The reduction in expertise required to perform these replacements would significantly reduce the cost of these operations while simultaneously reducing e-waste.
The number of people who might actually like this is very tiny. Most of them do product reviews. But their audience is not going to care. Think about your older uncle. Your niece in her 20s who loves to paint and read but doesn't want to replace hardware. That's what most people are like.
Those are the people who Jobs focused on impressing and enabling to do things they wouldn't do otherwise. That is the focus that has been lost without Jobs, IMHO, and it's the focus that makes the products better for people who want to get the most out of their products per unit of time invested in learning how to use it.