"You guys"?
Interesting. See, you are on a website populated by "you guys". What does that make YOU?
In response to the meat of your post:
A) Conventions do have bumps.
B) Romney needs all the votes he can get.
C) I don't expect this to be a Romney landslide. Too many 'takers' in America.
Perhaps I am in the minority here (although I doubt it), but let's just say in the grand scheme of things, away from this website, "you guys" are a small percentage of "us".
In response to your meat:
A) Conventions do not give 15% bumps ( 3-4 5-ish?) and Independents are what we care about - no one else matters; with that you must agree.
B) Given A, then: Obama needs all the votes he can get
C) Not all the "takers" from last time are going to vote this time. Many are long gone from their 2008 residences and are too freaking lazy to register again.