If I was going for the keyphrase green apples and my URL was greenapples.net would that mean I would automatically rank high for green apples? =/ If not, does it at least make it a lot easier to rank for green apples? (green apples is an example, please don't ask me why I made a site on green apples cuz I didn't xD)
Keywords in your url will Definitely make it easier to rank in the Search Engines. You will still need to do some SEO and Link Building... The amount of SEO you need to do, in order to rank high, would be defendant on the size and competition of your niche.