That may be all well and good, but most large agencies require *everyone* to carry the same service weapon, if for nothing else than it's easier to purchase one type and only one type of ammo for the entire agency (excluding swat/tactical/specialty). One of the other reasons is in an extended firefight (think Bank of America hold-up in L.A. several years back), field officers may need to borrow ammo from fellow officers if they've depleted their own supply, or if they have to cover another injured officer. Doesn't do any good when two officers side by side have different weapons, different loading mechanisms, and different ammo. Not to mention having to use someone else's weapon in a firefight--you want all officers to be equally trained on the same weapon.
Although I agree Reid would logically choose the revolver, no way it would ever be approved as his primary weapon for field use.