The more muted reaction on the vote question is likely due to interviews being conducted over a longer period of time. Gallup reports presidential vote preference for registered voters using a seven-day rolling average rather than the three-day roll up of adults used to report their job approval rating. If Gallup is picking up movement on their vote question to match the shift in the Obama approval rating, and if that change persists, the vote numbers should continue to move in Obama’s direction as well.
Most other prominent national pollsters have not been fielding surveys during the course of the two conventions, in part because of the historic tendency of polls to “bounce” up and down as the conventions are underway. Other daily tracking polls — such as the automated telephone surveys conducted by Rasmussen Reports or the new Internet-based survey conducted by Reuters-Ipsos — have not yet picked up a pro-Obama bounce.