I noticed this too, when I first started reading about this bug everyone was saying it would kick in around 5 mb, the number keeps going up. I agree that it is probably being triggered by a specific event, item or corrupt quest file that somehow corrupts the entire save. Whatever it is, I hope they find/found it and fix it soon, I haven't been affected yet but it still makes me nervous.
Yes, the save file thing is very inconsistent, but you do raise a good point. It might help things if the people who have the issue, would share everything they've done in the game. Which would include:
-Quest completed, and taken.
-Perks taken
-Items in your possession, or in your storage, including spells and shouts.
-locations visited.
How do we know this isn't a quest or item related issue? No one has asked this question before that I know of. Everyone immediately jumped on the save file/memory/caching issue, after abandoning some of the other theories, because the save file is the only thing that seems to be in common. Correlation is not causation.
There was a poster in the Xbox 360 section, who was experiencing lag issues after picking up a glitched key, and the issue was resolved when he got rid of the key. It was linked in one of the threads here yesterday.
Now let's assume what Pete said on Twitter yesterday is true, he vaguely hinted that the next patch is aimed at fixing this issue, and also added we won't have to start a new character if it fixes it. Could it be that these issues are simply related to glitched items, quest, perks, etc? And the general bug patches can fix this? Also when Pete was asked about the issue earlier this week, he said they didn't think it was related to save files, but they would look into it.
I've been here admittedly nerd raging myself about this, but I'm still not 100% convinced it's a save file issue. It could just as likely be glitched quests or items, it could be a manufacturing issue with the game discs. I don't believe it has anything to do with PS3 hardware, because people are reporting the issue with different console models, different hard drives etc. All we can really do is wait and see what this next patch does.