No idea. I wouldn't look into PSN game prices being too cheap, though. After all, a free online service prevents a huge revenue flow that a paid online service would have.
There have been occasional sales where games drop for a limited time, and there are a couple that had permanent drops if I remember correctly, but the majority are at their original price.
Yeah like Skippy said sometimes Sony will have what they call a "Summer Sale" and about 5 games or so will drop about $5. There have been a few legit price drops too I think.
