Most people outside the bitcoin world won't use changetip because they will have to buy bitcoin before to use it. And those who already know how to do that, will know how to "tip" from a regular wallet (even though changetip makes it easier).
Well, they do allow you to "top up" your account with a credit / debit card now. I think they've still got many things to work out, but they're building a pretty decent service I think. I hope it works out for them!