That said, VirnetX has also sued Apple about iMessage, so it's possible there's something to what you've said (but I've never heard it said before that Apple was going to open up iMessage).
Whether the culture has carried over, who knows.
Even as an iPhone user, I never would have thought iMessage was even in the top 5 or 10 reasons to keep using the platform. But I'm old, don't text all that much, and have unlimited SMS anyway.
I imagine all the cool kids these days are using alternative data-based services anyway. Snapchat, the like. For us old folks, WhatsApp, GroupMe, etc.
Yes and no, because friend groups are fragmented across services and iMessage or text is the common denominator, especially for group messages.
Apple doesn't make money through advertising they make it by selling phones. How does opening iMessages up to Android help them to sell more phones ?
[0] http://scripting.com/davenet/2001/04/30/strategyTax.html
As for google: I have no idea what is up with the stupidity. What people want is simple: an app that works on the PC and the phone, that can do messaging that falls back to SMS if the other-end isn't capable of "data" based communications, and ideally has encryption as an option and video chat as an option. Hangouts was like 90% of the way there, and then for some reason they went insert offensive analogy here and decided to release allo and duo with half the functionality. And oh by the way, after the release of those two apps, Hangouts started acting goofy for a month (which I struggle to believe is coincidence as much as I hate conspiracy BS).