That is just the problem with a system that has such a small userbase.
Small userbases are disproportionately made up of hard-core gamers; this means that they're very likely to own multiple systems and be very well informed. This gamer is going to be aware of reviews before the game is released, and may have played a demo, and if the game is not particularly good will not buy it.
That's the point. Lamer will not pay $800 for game machine... (ok, few kids bought Spider-man 3 but that doesn't count...) The quality bar is set very high but I think devs know it.