Must be just me or an American thing, but imessage isn't used nearly as much here; probably because Android takes up 80% market share, so people stick to cross-OS applications like Whatsapp.

It's because of two reasons:

1. iMessage interacts with SMS just like normal

2. It gives you the "blue bubble" which is a sign of higher class, because you have the more expensive iphone platform.

This has been beat to death, but another perspective is that the blue bubble indicates a better level of service, and is thus preferred. More reliable, faster, better media sharing, etc. Green bubble means the opposite because sms is a vastly inferior user experience. The shunning of green bubble people is because if one person on a group chat is a green bubble person, that ruins the blue bubble experience for everyone else. It's not just arbitrary status signaling for me at least.

I typically use an Android phone. If I use any of the multitude of "over the internet" instant messaging platforms, we all get the full level of service.

But if someone messages me from iMessage, I can only reply via old school SMS/MMS because Apple won't allow any non-Apple users access to their IM platform. This is incredibly annoying and well established as an intentional selling point.

All I hear is "if you want me to really listen to you, then you need to buy a specific brand of device."

A "green bubble person" is just someone forced to use crappy fallback measures because your preferred messaging platform wants to be exclusive. I'd gladly install iMessage (as I've installed many other IM apps) if it was an option, if only so I could stop the endless complaints about "green bubble people" ruining everyone's day.