GB have nothing to do with the blu ray. I have a 320 PS3 so it stores much mopre data although I would reccomend getting higher than the 160 Gb because just like computers they get slower as the fill with data. Furthermore some games will require a large amount of updates which take a bit of memory and also some games will not play well on a lower GB of ps3.
For the blu-ray films it is not a matter of GB, it depends on the P. X-box is only 720p which is HD Ready (Can be used on HD Systems to a good quality) whereas 1080p is full HD and gives optimum quality to both the DVD and Gaming experience.