the difference is that the SSBB hype is mostly self generated(besides the Dojo site, and even that can be considered self generated) Halo was planned hype by a massive marketing campaign. I am sure Halo would have been major hyped with the ridulous marketing campaign, but not half of what it was.
End of 2009 Predictions (Set, January 1st 2009)
Wii- 72 million 3rd Year Peak, better slate of releases
360- 37 million Should trend down slightly after 3rd year peak
PS3- 29 million Sales should pick up next year, 3rd year peak and price cut