Ok, lets start off with fact A. When advertising as 120 gb, they are using the stat that 1000 bytes are in a kilobyte, versus the truthful 1024 bytes that are in a kilobyte (your system is showing you the value based on 1024 bytes in a kilobyte). This means that with the true value of a kilobyte, your system is actually only 111.76 gb, not 120 gb.
Now lets go towards your current save files. Based on what you mentioned, you have approximately 7 gb of stuff saved, but as previous people stated, you show you are playing BFBC2 and Red Dead Redemption as well. I have no clue what those games take, but it is probably a considerable amount. I may be overestimating or underestimating, but you probably have ~10 gb of save data. This brings you down to 101.76 gb. This leaves approximately 20 gb that are still unaccounted for.
The ps3 system saves 10% of the hard drive space for its own things, which would be 12 gb. You are now down to ~90 gb, with about 8 gb still unaccounted for.
The only thing I can think of is RDR and BFBC2 taking up more space than I previously mentioned. I believe BFBC2 takes a little space for a mandatory install of some sort. RDR also requires some install to the best of my knowledge. Updates for these games and everything else, I really don't think you have to worry about anything...it's completely normal.
Money can't buy happiness. Just video games, which make me happy.
