iPhone/iPad linking to Mac for iTunes is pretty seemless. You plug it in and pretty much have drag and drop capability. Plugging Android or some other device works well enough via USB and you copy stuff over but having the interface there and ready to go is great. Signing into each device with one account that gives you access to purchases directly is great. Media on iTunes is fairly competitive price wise and Apple is a leader when it comes to securing exclusive content which is great.
I've used just about every combination of OS and device and Apple is definitely the company that has thought about how to make all of it work together out of the box. I simply dream of Chrome OS and Android working as well together as iOS and OS X do. Simply put though, Apple still thinks about doing things locally: you buy your media, you download it, you're all set. Google wants you streaming stuff so you'll stay connected to their ad servers. That's fine and Google Play has a good interface but I still have enough times where I'm out and don't have immediate access to wi-fi and would like to enjoy my content.
I used to use (well still do really) Amazon MP3 for music. That's fine, buy your CDs from Amazon, get the mp3s. Well they don't have everything I want so now I have to upload to their server and redownload on my devices. It's all very awkward to sync and the amount of content I can have in the Cloud is limited. So I end up using my iPod as it's easier to manage my content in iTunes and copy it over (which is quite seemless). I'm sure there are other quality media managers out there for OS X and Windows depending on the devices you use, but with Apple you get it out of the box so why look for something else?
Apple devices tend to be competitive on price as well, outside of Macbooks which have no real low cost alternative but iPads can do most of the basic work that a low-end Macbook would provide so that's all good I suppose.