You have to look in the past to understand why this is good news. Yes they are still expensive now, but don't you remember when a DVD player use to cost $500, and now you can get one for $30,and you can get 100 DVDs for $20. Yes a HDD is cheaper now but eventually BD will be cheaper.
And what this 120gb in a disc means. Think about this for example, in the past when digital cameras came out a 1.3mp camara was a good quiality, today that's crap! you have people taking pics with 7,10 even 15mp cameras, what if somebody ask you to burn those vacation videos and pics in a disc do you think you can fit those pics and videos from a 15mp camera and HD camcorder in the same space that it would take from a 1.3mp camera... NO!!!!
And you are not going to say here I'll put them in my 2.5" 600gb HD you can take it. Instead you will be able to burn those 2000+ pics and videos from a 15mp camera in a one BD disc that probably cost you less than 25 cents. Ofcourse this might take years to see. And remember now is 15mp pics and 1080p video but we are already entering the 3D era so pics and video files are only getting larger. Just my 2 cents. Still, today a portable drive is still a cheaper option.