It isn't a matter of "telling the truth" or "lying" as much as it is particular developer's opinions ...
Ubisoft tends to use a lot of middleware which may or may not be well optimized for use on the PS3; the developer of that middleware may have made assumptions on its use which will impact performance in various ways.
It is likely that Ubisoft is using the Unreal 3 engine and it is possible that the scripting in this engine does not take much (any) advantage of the SPEs; the end result is scripting (AI) would generally take far longer to process in the PS3 version of a game than the XBox 360 version of the game.
Obviously Sony developers wouldn't have issues because they are focused entirely on the PS3 version of the game, any middleware they have the source for can be modified to increase performance on the PS3 (something you wouldn't want to do if you were producing multiplatform games), and they will have access to engineers who can help them optimize everything.
