Watch Grenade be the #1 song of 2011 anyway even with these newer smash hits.
All year-end #1 songs for the past 12 years were released on or before March 30th of the year, so I don't think any new release from this point forward has a shot. It would have to be really really massive, even bigger than I Gotta Feeling which released in May but ended up at #4 at year-end.