I don't think it is related to the memory what so ever only because, I like you own the same 120GB slim PS3 and my game freezes whenever I do the following:
Go Into V.A.T.S.
Enter a building
Speed Travel
Try to Buy/Sell something
I don't see how doing any of those basic tasks could be related to the Ram on the PS3. Even right after my game loads if I don't do anything but hit R2 instant freezes.
See, that right there is a perfect example of one of the almost infuriating mysteries surrounding this game.
The problems (bugs, glitches, freezes and crashes) are so varied and completely unpredictable that it just boggles the mind. I guess I just don't know enough about how software works. I can only imagine the amount of headaches involved in trying to sort out code in order to locate, isolate and repair so many problems. What makes it worse, in my opinion, is that for a lot of players (myself included) there just in no reliable way to pin down what is causing the freezing and crashing. I mean, seriously, for me there is no single location or series of events that triggers the freeze and crash. I've tried like mad to figure out if there is some sort of sequence of actions involved and there just does not seem to be any. I can repeat ... exactly and faitfully ... the actions I took right up to a freeze and crash, only to have the game continue to play and then freeze and crash at some other random point.
Right now, my friend is going in to his 13th hour and has yet to have any problems other than simple bugs like radscorpions stuck in rocks or an odd scripting bug here and there.
I'm not going to even try to defend Obsidian or Beth but I have to be honest and admit that I can see, even with my limited understanding of how programming works, the difficulties they face. As I mentioned in another thread, I think someone somewhere made the decision to release this game on schedule thinking that any bugs and glitches would be fixable in the same way as Oblivion and FO3's bugs and glitches were. Unfortunately, in this case, it seems that that decision has blown up in someone's face and no one really knows exactly what to say to a gaggle of pissed off consumers.
The whole thing is just a mess and it's a shame since I really think that NV is a great game.