That's how they all start out, nice and snappy in the beginning, then starts the degradation of parts. They (all manufacturers) usually start with great/expensive parts then slowly work down to mediocre/cheap ones. They usually make them smaller with limited hardware in order to push more units with cheap manufacturing costs.
I can almost guarantee you that if you change your blu-ray lens to an aftermarket one, you'll see huge improvements. This goes for all systems excluding the fat, the slim and super slim come with sub-par lenses in them that degrade quickly (a year or so?). GT5 is a highly data sensitive game which means the lens runs in over-drive (so to speak), it degrades lenses much faster than normal games.
I've had 2 lenses (on a 120gb slim) from Sony that both crapped out, the second one was only used for GT5. They both lasted around 6-8 months each, I got an aftermarket one installed, a year and a half later, no issues whatsoever (loading, anything).
