"The Arduino Diecimila (and the original Arduino NG) has a built-in resistor on pin 13. On Arduino NG Rev. C and pre-NG Arduino boards, however, pin 13 does not have a built-in LED."
Is this correct? Because the first sentence is taking about a resistor and the second sentence is talking about an LED. Shouldn't it be one or the other?
No, because they can have a resistor and NO led, or a resistor AND an LED.
Maybe it would be clearer by saying
""The Arduino Diecimila (and the original Arduino NG) has a built-in resistor AND LED on pin 13. On Arduino NG Rev. C and pre-NG Arduino boards, however, pin 13 does not have a built-in LED."