[jQuery] Curious as to why a fadeOut() won't work but a hide() does??

[Joel Taylor]

Hmm, I'm confused. I have a plugin which has this code:
$(this).submit(function(){
        $(this).fadeOut("slow");
});

And it doesn't fade the form. But when I change it to:
$(this).submit(function(){
        $(this).hide();
});

It does.

Why?