proof of concept: try typing this into the Chrome URL bar:

javascript:document.getElementById('top_div').style.display = 'None';document.getElementById('pmflashclient').style.top=0

The reason (theoretically, at least) you can do this is Adobe is sand-boxed; flash has to live in the embed object you frame it in or "go through channels" to get permission to go full-screen.  The best it can do to stop you from changing the container dimensions would (again, in theory if not exactly in practice) be to get in an arms race with you over control of your DOM -- basically DOSing your attempts to manipulate the DOM attributes by hooking change events (or polling unhook-able attributes) and "changing things back."  Nobody wins such a battle -- two can play at that game, but the user will just eventually find something better to do than paint trippy mouse-cursor trails into the void where their browser window is supposed to be   This is exactly what often happens when i.e., AdBlock Plus comes head-to-head with a site like The Pirate Bay that is determined to pop up some garbage windows at any cost.

I'd presume this is the same reason Google puts that "view on YouTube" button on cross-site swf embeds.  Google-hosted places are the only ones where Google can control the horizontal and the vertical, so to speak; any other site embedding their swf could be doing all kinds of silly shit to it, like plastering it over with ads (by accident or on purpose), scrunching it down into ridiculous dimensions, etc (both things I've seen happen on real websites).