Yes people can't be bothered to download an app like what's app then make sure all 100 of their friends have it downloaded too. IMessage just works automatically if data is on. For people who aren't tech savy and don't really care, (majority of people), it's brilliant!Do you use Hangouts, WhatsApp or any messaging app like that? iMessage is just like those, except it's built-in to the iPhone, which means people don't have to download a separate app, create an account, hope their contacts are also on the app, etc.
To me, the big benefit is the ability to message over WiFi. Of course, this only works if the other person has an iPhone, but that's the great thing: if they don't, iMessage will just use SMS/MMS. But if they do, the conversation will be encrypted and sent over data connection or WiFi. I get terrible reception in my house for some reason, so for reliability purposes, I've gotten immediate family on Hangouts. But most of my family and friends have iPhones, so trying to get others on there is a lost cause since almost everyone else they talk to also have iPhones.
People need to start looking at consumers more realistically. Imessage is a selling feature. Just because we all may be smart enough to understand what it's not really a big deal, to more consumers than not, it is. And it works really well. Something like this for Android would do wonders. Android needs to take one small teeny tiny page out of apple's book and make things a little more simple for the average folks.