I'm just looking through the reviews for apps like infinity blade or angry birds and all I see is people giving 1 star ratings for things you don't even need to buy. They let you buy money in infinity blad which isn't even an issue in the game because it's so easy to come by. And in angry birds they added a giant eagle you can buy for a dollar that lets you skip levels but once again it doesn't affect anyone who doesn't buy it and the game is exactly the same before they just added a non essential thing you can buy. Yet all these people do is complain about how in app purchases are "ruining" the game when it doesn't actually change anything.

Some people are fucking idiots when they say oh, it wasn't the Mario game that I thought it was going to be then 1-star it because it wasn't what they expected it to be and because they didn't read the description.  Then reviews on something like the Flashlight app people are like wtf, it's just a blank screen then 1-star even though it does exactly what it was supposed to do.  I try to avoid them at all costs but I always look into them to get a general opinion of an app and end up just wondering why I went into it in the first place once I start reading some stupid comments.

Because it's usually stuff, both those games are examples, of things that are basically cheats to beat the game for you, when if you just played for long enough you would accomplish what you were trying to do anyway.  It's pay money because you're lazy.

It's honestly because people are ignorant.

The itunes store is pretty weird in how people rate apps.  I've seen people give games 1 star and say its the greatest game they've played.

People just naturally hate DLC for games that they've already paid full price for. Simple.

The same issues comes up from time to time on the android markeplace. Doesn't seem so common though. 
 
I hate it when people give an app one star and comment on how they'll come back and change their rating if the stupid issue they had with it is fixed. It's almost like blackmailing the devs, but in the most retarded and ineffective way possible.

Most people treat the 5-star system very much in the same way as like/hate. 5-stars if they like is and only 1-star if they don't, which is why youtube has changed to a like/dislike system.