Modern engines are running very efficiently. It is very, very difficult to overcome Americans perception that you need to change the oil every 3000 miles.
It benefits dealers, Jiffy Lube and other service companies b/c they obviously get more business the more often customers come in.

It does depend on your driving (heavy traffic, dusty conditions, etc) but 6000 to 10000 is fine on these new engines.
Dark color means nothing to the performance of the oil. It will darken very quickly and you can test it, the oil will have excellent protection.

Of course, it is easy to say change it often. It hurts no one. But it can be a waste of time and money as well as the significant impact to enviroment and waste.

check out bobistheoilguy.com for more reading on oil.