AC is a good example of what the PS3 has going against it.
It's dev tools are very difficult to work with causing long dev times(which means developers loose more money), various problems or in worst case scenario, scrap the whole project(Frontlines fuels of war was suppose to come out on PS3 but the devs decided to scrap it since they found the dev tools to be a nightmare to work on).
Long loading times or frame rate issues are another common problem as mentioned before. Now the loading times and frame rate issues aren't the fault of the actual machine, it is once again the dev tools forcing the developers to release the port before it's fully optimised(PS3 exclusives are fine on this area no doubt since Sony pay the devs extra so they have time to fix it). Loading times seem to be fixed by allowing the game to install certain files on your PS3.
MGS4 for example has to install each time you enter a new act. Now the first act takes around 10 minutes to install(seeing Snake smoke gets boring I tell you) but thankfully the other acts are faster, around 3-4 minutes.
AC is different, the PS3 version actually has a more stable framerate compared to the Xbox360 which can take a dip when in a large crowds.
But they did this by turning down the graphics a tad, same with Oblivion.
So when it comes to multi-port games Xbox360 is easily the winner leaving PS3 to survive on it's exclusives.
And the loss of Final Fantasy exclusive no doubt damaged the PS3 severely.