Fact is the ps3 requires more work to extract performance. So for the ps3 version to be so close to parity with the 360 version, they would have had to put in a lot of effort into that version. So many people, ps3 owners specifically, are so quick to claim the devs don't try or put effort towards the game in question since that's the easy mentality to have. Makes no sense to devote years and years worth of someone's life into a project just to be lazy or half assed about it.
The fact that files are stored differently on the HDD with the 360 could be reason alone why it doesn't happen on that version.
How do we know the game did not behave differently on their dev units? How do we know whether or not they had a thousand other, worse, bugs to hammer away on the ps3 version and just ran out of time? The patch is in certification already for both systems IIRC, that's quite a quick turn around for a patch so close from launch, now isn't it?
You can go ahead and assume that their QA neglected the ps3 version, but IMO we don't know nearly enough to make such assumptions.
What does that have to do with Bethesda when they aren't the team that ported Oblivion?