XBOX 360 discs don't have the capacity of Blu-Rays, and as such they are much smaller (When the full capacity of a Blu-Ray is being used, that is)
It is what it is. You're downloading an entire Blu-Ray disc worth of content - it's going to take a lot of time and space on the hard drive. Even so, I'll still be getting it earlier than I would be if I waited for an Amazon delivery on Tuesday evening (UPS takes FOREVER to get here). And it would cost about the same either way after the $10 I'll get back on PSN.