I just looked up impedance, cause I wasn't sure if that was another word for resistance or something else, and I founf out it's resistance to alternating current.
So I guess that is why the leds will work? They're high-impedance because electricity can only flow through them one way?
If that is the case, out of curiosity, could one hook up low impedance stuff, like say, a switch, to those pins, without interfering with uploading sketches, as long as you placed a diode in series with it?