there's no difference. it's all a scam. you want to know the real difference between blu ray and DVD? blu ray discs can hold more information. that's it. the information is the same, one can just hold more of it. and since any dvd can hold at least 3 hours of video, there's no need to put more information on the disc, and it's not profitable to do it either. they are just going to sell 2 hour videos on every blu ray disc, and if it runs over that time, they will put it on another dics just to charge you for it.
and You know high definition? you know how it works? they film stuff in high def cameras and they show it on a high def screen. Only problem, most things aren't filmed using a high def camera, so it makes no difference. and then there's everything that is over 5 years old, none of it is high def, it doesn't make any difference what you play it on, the quality is the same as it ever was or will be.