Due to the ease of reproduction, you really can't. That's why we really shouldn't rely too heavily on that analouge for comparisons. You can't clone 1000 more insteances of your lego set, you can't upload your lego set to the internet to be cloned further. Even if we get to that point in 3d printing, "pirating" a lego set properly requires resources to your 3d printer to produce those legos. Materials you may not have on hand, or that cost just a much as buying the lego set yourself.

>If they offer something where they deserve the right to take it back for any reason, then "buy" is not a correct word here, and the button should say "rent"/"lease" or whatever, but not "buy".

You could make that distinction, but the colloquial mind treats "perpetual rental until we are forced to remove content from servers" as "buy". both types of purchase go down once that part of PSN servers decide to shut down like they want to do soon-ish for PS3/Vita (they wanted to do it last year, but consumer backlash delayed it).