Ah, I see what you're getting at. By using the internal pullup resistor I can sidestep the external resistors. Would this have any implications for battery life, though, since I would now have to supply a constant 5v except for when the button connection is broken (open) and electrons diverted?
It seems like almost every Atmel chip has support for internal pull-ups so it's also future proof should I decide to switch chips. Great solution, thanks!