You are not an average user, most people change phone all the time, just as you said. I just pointed out that the possibility for having a phone for a long time is better on android (because of battery and memory cards mainly). If you can keep your battery for 7 years -- lucky you -- my 3 years old battery is not as good any more, and I plan to buy a new in the future.
It is not that it cannot be done on iphones, it is that it is *specifically* designed to be as hard as possible to do. This is getting quite common on android phones as well, but you can still *choose* top android phones with SD-card readers and replaceable batteries.
I applaud you for not wasting the environment, but it is certainly not thanks to Apple. Credit where credit is due, and here it is to you. I also believe on average, iphone users keep their phones for a *shorter* time as they see their phones as fashion accessories (this is only a feeling of mine, I have no hard data supporting it).