What was the average time it took to complete the game, again? 1.5-2 hours or so?

It's hardly a "full-fledged" game then and although they did lower the price, it still seems like too much. 20$ probably would have been perfect and I'm sure it would have been able to sustain more legs considering not just mostly fans of the series would buy it at that point, but many with a PS4 considering they'd want a game to play and the price is not horrible.

No, if practically anyone tries its most likely they will crash and burn, MGS is an exception.

I've played it. Haven't beat the side ops yet but I can safely say that it is NOT worth $30. You're better off waiting for a sale.

I'm sure if the game was part of a big IP, it'd be pretty easy to do. For example.. Uncharted or Halo.

If that's the case I would argue that it already has been done in Halo Wars but that is quite debatable in and of itself.

I must contest that unless these "prologues" don't have multiplayer, they could harm the the games they preceed.

no, I will wait for Ps+ free version before I play it.

It's pretty obvious that the only reason it's $30 on the PS4 is because it's on the PS4 which begs the question so why isn't any other cross platform game $10 more on the new system. 

And that's more of a why, because they can get away with it kind of thing which is pretty cheap, but no one is forcing anyone to buy it which is why it only sold a half million copies instead of the millions that MGS games typically move. 

My first inclination was to just pick it up later. Why not even pick it up a month or two before Phantom Pain releases? But the fact that I have yet to see a retail copy on shelves makes me wonder what type of retail distribution GZ is receiving and maybe more importantly for someone who just wants a hard copy for a collection, are they planning on keeping it in print or just letting it transition to DD only, which actually makes a lot more sense for a partial game of its length. 

Very few franchises can get away with this. 

If they want to try and sell a prologue, which is not a demo as it contains material that will presumably not be on the full game, it could actually lose them money to publish and distribute copies to retail. Charge $30 and no one buys it. Try and sell a demo that will be in the retail game and the publishers run the risk of losing sales when the $60 game releases due to consumer backlash. 

Games like MGS and Gran Turismo or Halo and Gears of War are among the small company of franchises that generate enough fan interest to warrant a teaser retail release. 

I haven't played it, so I can't say for certain, but I would imagine that no "demo" should ever be worth $30.

Your avatar reinforces your first statement. But to answer your question, the other cross platform games aren't overpriced because they aren't new games and people would notice it immediately. Konami got away with it because the MGS fans have been waiting a long time for something, for anything.

It's obvious that Ground Zeroes was aimed for a digital distribution. If you ask me, a game this short does not deserve to be made a hard copy. It feels more like an add-on to the main game, The Phantom Pain. But it's (kinda) good that they have released this game on a disc to offer more options.