Why don't the polling and media groups oversample republicans based on 2010 turnout?
Because its not conveeeeeeeeenient to them or their goal of scaring potential Romney voters into staying home.
Note that the perception that Obama narrowly leads could easily be used by the Dems to allege vote fraud by the Republicans (talk about the pot calling the kettle black - oh, I'm sorry, is that RAAAAAAACIST?). We need to be very careful about this - because if it is close we'll have an instant replay of the 2000 nightmare, this time accompanied by nationwide riots.