I agree- checking all of your old posts would be silly. But, when someone edits your statement, it appears as a modified/marked as new blip within the wave. The wave is essentially marked as new until you acknowledge this edit. You are therefore specifically notified that someone has modified your words. I would think that knowing you are likely to get caught in an attempt to sneakily change someone else's words would deter you from such an action. Its not entirely unlike a tracked change in a word processor- you are notified of a change and you accept the change when you acknowledge the changed blip.
Again, not the point. Between the time it's edited and the time you catch it, somebody has put words in your mouth and when your name is on a post, you are endorsing it. It's just a flaw of the Wave. If you could grant permission to editors of your choice, or the Wave starter, that is another story entirely. But when any random can put words in your post, it crosses a line.