it was excluded because it breaks the absraction of a "wallet". users do not need to know what a change address is, nor do they need to know what inputs or outputs are. this is the same reason why paypal/ach/sepa transfers do not disclose their internal implementation details. having that feature in the client complicates application design, and adds the burden of wannabe power users asking for support.
Given the current system, we still have users, who know their way around blockchain.info or another block explorer but haven't learned the "change address" concept ("wannabe power users" as you would probably call them; I'm not that blunt), getting confused and, you guessed it, asking for support.
This may not be the place to delve into this, but to elaborate: If there were an internal implementation requirement that change addresses must be used, you are right that it should be abstracted from the user. Unfortunately people have perfectly valid reasons to sidestep that abstraction by going to a third-party service that doesn't know what their change addresses are and therefore can't abstract it for them. For this reason (and the fact that random change addresses are not a hard requirement; only semi privacy-enhancing), my argument was that we should consider abolishing change addresses by default and just send change back to one of the spending addresses. This still has potential for confusion, but I think less than seeing a destination address that the client intentionally hides the very existence of. At least the confusion will hopefully not be the panic of "some random address hijacked most of my coins when I sent a few!! this address is not listed in my client anywhere, I have never seen it before, etc."
It is either a technical change like stopping use of random change addresses, or trying to teach people why it's good that their spent coins get shuffled into random addresses that they didn't create themselves and are currently discouraged from viewing. Which is easier? Does the average user even agree with the rationale of change addresses?
