Don't know about the others, but I have an iphone and a mbp. I used to have android phones before this, and I bought the iphone just to check it out, since I got a good deal on it.
For me, the "seamlessness" opened new possibilities of use. What I really love is being able to use the phone from my computer. I don't have to have it handy.
Examples :
1. Call and take calls directly from the computer. Extremely practical with corded headphones I use for listening to music. Could I just get my headphones off and grab the phone? Of course. If I noticed the phone ringing.
2. Handle messages from the computer. I don't send and receive messages that often, but for some random 2FA over SMS this is just so practical. Could I grab the phone and read the code? Yeah, but if the computer does it automatically it's much nicer.
3. The Handoff feature, for example when I'm on the bus, start reading some article on some website. When I get home / at the office, I can open the page on the computer. Couldn't I copy the URL and type it in? Of course, but it's clearly a pain.
4. Internet sharing: just activate it from the computer, don't have to copy the password, etc by handling the phone. As above, I could of course do this by hand, but it's much more practical.
Maybe all this could be set up somehow with Linux / Windows and maybe with android too. I honestly don't know - my windows PC can't even get internet sharing via usb out of the box (didn't care enough about this to look into it more). It works fine on Linux though.
It's not a question of having a short attention span or of doing something very difficult. It's just having tools that work for you and getting out of your way. After all, that's why we use machines (which computers are): to automate things.