It definitely depends on the design. One could argue that holding a huge arsenal would be completely unrealistic in the game where the protagonist has Wolverine's regenerating powers, but it's also a very easy thing to screw up....So easy that even the best developers do it. For example, "oh hey, there's a helecopter attacking me, but there's also these conveniently placed rocket launchers surrounding me".
Unreal tournament, Duke Nukem, Resident evil, Doom, quake all would suck hard if there was a 2 weapon limit.
Games like cod don't need more than 2 weapons anyways because it takes zero effort to pump 2-3 bullets into your enemy. Most games that only allow 2 weapons at a time (excluding halo series) are nothing more than camp infested\shoot from behind war games.
I hate to admit it, but I'm a graphics whore in denial.