Yes you are correct- the oil only needs to be changed about every 12-20K miles according to your driving habits. I don't know why this is but I can say that it is a testament to BMW's extraordinary commitment to being better than the other cars rolling the planet. My brother's 540i only goes about every 8K miles between oil changes.
I go by the indicator, as should you. By the way if there is any chance you can change your order to a 330 I would highly recommend it because having driven both I consider the 330 more than worth the price gap
Later dayz