[PlasmaKrab]

I have included some heavy artillery rockets and short-range TBMs in some OOBs of the Cold War Mod, though they are always restricted to player-only use.

The main goal is to have them available to scenario designers who don't want the trouble of editing and shipping their own OOBs. In some special scenarios, it can be useful as a first strike, say when you are defending or mounting an infiltration against a highly strategical place. Not at the center of the scope of WinSPMBT, but still interesting from time to time and technically feasible.
As a little bonus, you can use these systems as the ultimate counterbattery unit, as they have more range than any arty and generally enough HE kill to wipe a complete battery off the board.

Just to be clear, I'm only taking here about tactical artillery rockets (more FROG than Scud) or more modern short-range TBMs like the MGM-21 Lance or the Russian SS-21 Tochka (again, not Oka or Iskander).
As stated above by everyone, real ballistic missiles have nothing to do in a WinSPMBT game, and are absolutely not possible to model realistically, both in terms of accuracy and firepower (and I'm only talking about conventional warheads).

A corollary to the modeling problems is that these things are bloody useless in game terms. A handful of 500kg HE warheads falling all over the place with an accuracy more in the FROG ballpark may destroy a building or two and dazzle some troops, but they are much less battle-winners than regular arty. And strike aircraft at least do some aiming before dropping the same amount of ordnance.