If Amazon wants to take the hit to promote their store, it's their choice. Sales and price matching is a choice stores make to retain customers. PSN store has the luxury of being first in line and doesn't need to do that. They already get their normal cut from Amazon and can do whatever they want in their own store as it's right there on the dashboard of the OS.
Actually price matching with Amazon would only give Amazon less reason to promote those games, cause what's the point. Spend money on advertising the deals for customers to turn around and get it from the psn store anyway.







