Yes, Apple execs thought that iMessage exclusivity would help them. Perhaps it did a little but the app still connects seamlessly to android users via sms. I never think when contacting someone, “oh wait, do they have an iPhone?”
As for imessage-specific features (iMessage App Store, cash, imessage for businesses etc): they have pretty limited use. And in fact Apple’s choice inhibits some of them (like iChat to your business) which seems like an own goal.
More importantly, Whatsapp has crushed most of the messaging apps, imessage included. Apple doesn’t seem to care or try to block it.
So what offense, exactly has been committed?