No inherent protections, just different incentives. Storing a 4MB image at 80 bytes per $0.08 OP_RETURN transaction would cost you $4000. Why would you do that when you can use namecoin for practically free?
Which makes the statement you made that, "this currency stuff is frankly kind of uninteresting to me," kind of funny (I assume that was on purpose) because the currency stuff is exactly the thing that makes bitcoin work so well.
I made that statement because a lot of people don't realize that Bitcoin, ignoring the fact that you can trade it, has solved a fundamental consensus problem in distributed systems that we should care about and use :)