I think it's pretty much common knowledge, both sides are courting the Hispanic vote (border control), taking a hard stand on abortion is going to alienate on one voting side or the other, as will gun control, welfare reform, and gay marriage...
Going after the 'economy' and health care are the two that are popular with the population in general.... Heck, they aren't even bringing up Iraq/Afghanistan very much of late...
The general news media is so heavily in the pocket of Obama that they don't want to bring up the really important/controversial subjects and the McCain camp is willing to play along with them...So they don't have to worry about alienation either...