Sorry, didn't really want to nitpick...
R&C runs 60fps pretty constant 95% of the time - with only dips in extreme cases like when there are many things happening on screen at the same time (somewhat user provoked) or when loading is going in the background, i.e. when Ratchet jumps from one green platform to the next over a larger difference. This doesn't hamper gameplay in the slightest and qualifies as a true 60fps title.
The rarest games will have constant 60 fps (or any framerate), never dipping below that, for that matter - perhaps racing games being the exception to the rule, as they are also a lot easier to get constant. The more complex a game is, the more difficult it is, to lock the framerate - or in other words, the amount of action that could be triggered by a users action. In a racer, there are practically no things a player can do to trigger more action on screen than the engine is capable of - unless the engine is already running over or at its limit most of the time, it will be easily a constant framerate all the time.
A 3rd person game is probably the most demanding type of all and therefore the most difficult to achieve a locked framerate, simply because the player has an imense amount of possibilities to put load onto the engine. I.e. run through the level to find as many enemies as possible and make them follow you to the same spot and you may end up with more enemies and action going on than the engine can crunch within its time limitation.
The more freedom you have, the more unforseen events can happen that could cause framerate issues.
R&C does an excellent job and is as constant as one can get for a game like that. In that sense, many of the 60 fps R&C games on PS2 were not worse, nor better. They all qualify as true 60 fps games.
COD4, while having some framerate issues here and there, is a 60 fps game as well.
Cheers Phil