Rob Goodspeed analyzes how many words each candidate's website dedicates to each issue. You can see that John McCain has very little to say outside his security/Iraq/veterans comfort zone. To me, that means it's vital for Barack Obama to try to hit McCain early in that comfort zone since that's where it'll be hardest to build an argument that convinces people, but I think Democratic strategists have a bad habit of preferring to stay within their own comfort zone.