Halo 4 for the next console is more wishful thinking than logical deduction. MS' next console isn't coming out in Fall of 2012, and they wouldn't launch a Halo game (now that it's an established franchise) on a console that will be supply limited for the fanbase for up to 6 months. As you said, the trailer even had the 360 logo at the end.
If people honestly believe that they would include a beta key for a next gen title in a current gen one, there's probably no convincing them otherwise.
Edit: Who is allan-bh and why did his post spark such a reaction?