I think you'd be better off if someone geve you more info on how to forge a productive, meaningful life for yourself, and those other questions will answer themselves. For instance, once you move out of your parents' basement and start paying your own cable bill, you'll notice that HBO costs $200-$300 a year, not $20-$30 a year as you seem to think, and their shows have historically had very lo-o-o-ong hiatuses, so if you're only subscribing to HBO for two or three of their shows, it's probably cheaper in the long run to buy them, even at iTunes prices.
And once you move to an actual multi-room dwelling with - gasp - maybe a spouse and kids, you'll find quite a bit of value to having your content readily available on multiple devices, and not tethered to an optical disc and whatever TV you happen to have a Blu-Ray player connected to.
And most of all, once you have elevated your existence from shut-in to productive, dignified human being, you'll understand that your time on this earth is actually valuable, and you'll become more annoyed by the time-wasting nonsense that comes with watching Blu-Ray discs: loading up discs, cueing up partially-watched episodes, navigating menus, sitting through interminable and unskippable content (trailers, merchandise commercials, piracy warnings, and my personal favorite, commentary track disclaimers). And you'll realize - again, keep in mind that your time will be actually worth something in this scenario - that you might even be willing to pay a little extra to avoid all that.
