Sure, but let's not fool ourselves. It isn't exactly a cost center for Apple to run the service nor would it be to scale up usage to include Android users. The cost would be a rounding error to Apple.
From a business perspective, I'm much more sympathetic to arguments that iMessage is a perk Apple wants to keep as incentive for more users to switch to Apple's ecosystem and, likely more important, lack of cross-platform interoperability raises the cost for existing Apple users to transition to Android.
Another way to look at it is that there would always be a fixed cost to operating any global messaging network that would probably be at least a million dollars a year. Piggybacking on Apple's already-built network and focusing only on marginal cost sidesteps the reality that standing up a service that big from scratch is very expensive. Even if iMessage were a decentralized network like email that allows federation, Beeper Mini would be on the hook for a much bigger bill.
From a business perspective, I'm much more sympathetic to arguments that iMessage is a perk Apple wants to keep as incentive for more users to switch to Apple's ecosystem and, likely more important, lack of cross-platform interoperability raises the cost for existing Apple users to transition to Android.