Yes, HDDs/memory sticks are cheaper, but DIFFERENT
Using a memory stick/card/drive or a hard disk drive to simply MOVE data is one thing, and clearly more cost effective than a BluRay disc.
But I don't think anyone would buy a HDD or even a memory stick in order simply to give a copy of some data to someone else, especially if the data was required to be read-only (or at the very least is NOT required to be updatable "in situ" on the media.
If nothing else, the cost effectiveness argument starts to fall apart in some situations.
A 250GB HDD may be a cheaper way of handing out 250GB of data, but it's an expensive way of handing out 80GB.
And as for video/movies being the only application, I seem to remember that the same thing was said of DVD "back in the day" (not necessarily by this site). The one thing that is clear from the history of data storage technology is that applications soon grow to fill the capacity of *any* available storage tech.
This device should have been reviewed on the basis of it's execution of the technology, not the reviewers opinion of whether the technology would be of use to anyone.
That's for those other people to decide, based on what they need from the technology - the reviewers job is to help such people decide which execution of the technology is the better investment for them.