and a 4.7k pullup resistor on RESET.
The internal pullup by itself isn't reliable? Surprising.
It's "weak". 30K to 60K ohms. In some situations that makes it unreliable.
And, the cost of a single 4.7K to 10K resistor is how much?
I was quite surprised by this, too. The only thing I can think of is Atmels obsession with power consumption. I'm guessing the extra microamp that a lower resistor would consume keeps Atmel engineers awake at night.
Only unwashed people with filthy, dirty power supplies would need 4.7k pullups.