i really don't think it's an issue of bandwidth or hdd storage space, as per the claims made
i think it's more their investment in selling blu ray, as well as people finding out that the vast majority of those 25-50GB games are filled with padding because of the slow drive (a lot of the 360 full game downloads are smaller than they are on the disc, as well)
seriously, you're not going to be downloading 50GB games because 50GB games don't exist for you to download
i like discs better myself, but if one of your selling points is a huge hard drive, you should maybe sell some games to put on it