I think the Steam global stats in general go to show how many people are buying games, playing them for a few hours, and then forgetting them. I don't think it's necessarily a flaw in Aquaria, since a similarly small percentage of players are getting beyond a few hours into other Steam games as well. It may APPEAR more shocking in the case of Aquaria because a few hours = Open Waters, whereas a few hours on a game like Braid or World of Goo = half of the game.
I think it's more an issue of attention; many of the young kids using mommy and daddy's credit card to buy games simply don't have the attention span to finish a game that isn't full of guns and explosions and boobs, ultra-stimulating sorts of games that have been market-researched specifically to cater to an audience that gets bored very easily. Similarly, a lot of older gamers who have the finances to buy a crapload of games don't have the time or attention to devote to more than a few hours of gameplay. But again, I wouldn't say it's a flaw in Aquaria or in any of the other games.... unless all games are constant flashing lights and attention-capturing cutscenes, much of the audience just isn't going to be able to sustain attention for long enough to enjoy the full experience.
Of course it's unfortunate, all developers hope that all the people playing their games are playing them from start to finish... but it's simple fact that there are a lot of people who don't do that. I don't believe that the solution to this lies in lowering the standard so that all games are easier to accommodate the seemingly increasing percentage of the population lacking the ability to attend to a task for more than an hour or two. I think the problem is far more fundamental than a lack of perseverance in games, and the problem should therefore be addressed at its roots instead of covered up (and indeed encouraged) via unchallenging stimuli.
