Photostream only shows your last 1000 pictures, it isn't a means of backup. The op asked how to get the photos on his mac - the easiest was is to just import via iphoto... done. How he backs up his mac is not relevant since that isn't what he asked about.
Probably poor wording on my behalf. I use photostream as the vehicle to the Mac. Someone else posted a better explanation.
I wasn't talking about backing up the Mac, but rather the photos on the Mac. Hence why I asked the OP.