Valve has adjusted it’s Early Access FAQ to reflect the harsh reality of Early Access games available through the distribution network.
Previously, the FAQ but the decision of final squarely in the hands of the developers
It’s up to the developer to determine when they are ready to ‘release’. Some developers have a concrete deadline in mind, while others will get a better sense as the development of the game progresses.
Now, however, the wording has changed to reflect what could happen
You should be aware that some teams will be unable to ‘finish’ their game. So you should only buy an Early Access game if you are excited about playing it in its current state.
Early Access to games did not start on Steam. Both Mojang’s Minecraft and Introversion’s Prison Architect reaped great financial rewards with the practice away from Steam. This did not stop Valve from taking the idea a step further and dedicating a whole section to the practice with some games like DayZ and Rust making millions through their unfinished products.
You can read the full updated FAQ at http://store.steampowered.com/earlyaccessfaq