$30 isn't full game prices, it's 1/3rd of what you would pay for a physical copy of a game down at your local game store.
I think this logic is a little flawed. Maybe 5-10 years ago this would be true, but these days only AAA games (excluding special/collectors editions with useless bundled crap) are around that price range. Most games are around the $50-$70 range last time I was in a games store.
And Day-Z isn't a big budget AAA game, and he didn't buy a physical copy of the game in a store - he bought a digital version on steam. Compared to other games on Steam, $30 is very much full game price.
I haven't played Day-Z so I don't know how good or bad it is, but I see nothing wrong with 'early access' itself. The games are clearly labelled as being in an unfinished state. The devs are releasing it a little early to fans that will be willing to put up with the bugs, in order to raise a bit more cash to finish the project. If you don't want to put up with an unfinished game and want to wait until its finished, don't buy the damn game until its out of 'early access'.
There is always the risk that they will take your money and not finish the game, but that's the risk that you, as a discerning buyer, must decide to accept if you buy the game. Caveat emptor.
(Much like nearly all those kickstarters that took heaps of cash and never delivered, but at least this one has made it to beta stage.)