I haven't seen it that and I am checking server logs of various sites. Because you would expect the bot to index the form's action tag which is going to be a valid link anyways. And I never saw that with POST forms.
Now if what you say is true then is going to open a new world of comment spam, injecting any kind of element/tag with a link eg:
<font href="http://example.com" /> having google to follow them. That's something I haven't tried.