I usually use the "car warranty" analogy. That "free" 3 year service plan is not free. It's just built into the price. We're just more transparent, that's all. I like you're "typo" example as well.
The "facts of software development" is really important, especially if the client hasn't got a lot of experience in developing products. I've always found the more experienced a client is, the easier they understand the concept.