This is not true at all, I have an iPad (and it's the only device from Apple I own). I could throw it out the window tomorrow and buy an android or a Surface.
I do everything online, with apps only giving me a better view to the online content:
- feed reader
- evernote
- mail
- maps
All of these are replacable by either a mobile website, or an application on android or windows that does the same.
Some games I might miss, yeah, but that's not a deal breaker...
The only cost for me to get out of the eco system, is the same as getting in: just buying another tablet.
That being said, I like the apple hardware, it can take a punch, and is very stable. unlike the android devices I've owned.
I do own a WP7 but have sworn not to give MS a cent again, after they told me my top of the line hardware will not be receiving an update merely 2 weeks after I bought it. For a gadget freak and early adopter, this is a serious kick in the head.