Hard drive storage is cheaper per GB (~$A0.12) than BluRay storage (~$A0.60), as well as being 'on hand' (unless you have so many HDs that you can't have them all hooked up, in which case you'd start investing in external HD cases), unlike BluRay where you have to find the disc with the file you're looking for, put it into the computer, etc.
Yeah, it's more portable, but how often are you going to be taking disc #8 to parties just because there's one video on it that everyone likes? And how many people have BluRay players (yeah, there's starting to be quite a few, what with the PS3 and the geeks with one in their computer, but I'm talking more about the average person)? You may as well just burn the file to DVD when you need to, and save money.
/ Or, if you're a real cheapskate (heh), you can always bring an external harddrive.