Varied NPC AI in left 4 dead?

Do the different characters have different AI behaviors?

While playing left-4-dead with two of my friends we endless joke and complain about Coach's sniper shotgun. He seems to last hit special infected from extreme distances with a shotgun.

Obviously, his super-human aim is attributed to the fact that he's a bot. But what about his preference for a shotgun? How about his bias towards killing special infected over common?
Rochelle on the other hand seems to prefer to mow through common infected like a meat grinder with an automatic rifle.

Is this just me seeing a ghost in the machine or is there more to it?

Each of the AI bots (in L4D and L4D2) do have preferred weapon types that they will always try to use, depending on what types and level of weapon is available.

Shown here as Level 1 Preference / Level 2 Preference:

L4D Survivors

In L4D

• Bill: Submachine Gun / Assault Rifle
• Francis: Pump Shotgun / Auto Shotgun
• Louis: Submachine Gun / Assault Rifle
• Zoe: Submachine Gun / Hunting Rifle

In L4D2

• Bill: Submachine Gun / Assault Rifle
• Francis: Pump Shotgun / Hunting Rifle
• Louis: Submachine Gun / Auto-Shotgun
• Zoe: Submachine Gun / Assault Rifle

L4D2 Survivors

• Coach: All Shotgun variants (both weapon levels)
• Ellis: Submachine Gun / Hunting Rifle
• Nick: Submachine Gun / Assault Rifle
• Rochelle: Submachine Gun / Assault Rifle

Source: L4D wikia
(specifically the character-specific "main article" pages linked from this source)

Afraid I can't comment on if there are any preferences regarding selection of targets, or inhuman accuracy...