It's a nice idea, but I doubt most people actually do that. Also, it still kind of leads to a blown up score based on "potential" and when I'm looking through the highest rated games I don't care about potential, I want something that is good NOW.
This confuses me. It is good now. There is an interesting plot, well done characters, and a creative concept. It's like reading the first two chapters of a serial (comic, manga, book series, etc.) If they suck this early on, I won't finish it. If they are good I will keep reading it and let others know that what is published so far is worth reading. This is pretty much how professional writers have gotten their starts ever since printing began.
Is some of it based on potential expectations? Sure, but those expectations are based on the proven experience so far. Could it go downhill? Sure, but until it does you shouldn't slam it when what is available is very well done.
If it doesn't have sufficient of the content you are looking for, then hit a different game until enough content you want has been released, but don't fault others for positively rating something they are currently enjoying.