).Couple things, a halogen is a type of incandescent lamp. As such, it is fully dimable. The difference is that a halogen has an inert gas sealed inside the glass with the filament. This is like arc lamps, which also has gas sealed in them, but are under much higher pressures. Halogens have some pressure, but not nearly as much as arc. This is the reason for the explosion warnings on arc lamps. Because of this gas, the filament can operate at a higher temperature (aka more amperage) then a regular incandescent lamp. This is also the reason why a gas leak will cause halogens to not work, they burn out instantly/don't turn on at all. This is normally seen as a discoloration on the glass surrounding the filament.
Second, you can have more then two flags in a mechanical dimming system. This is more costly and adds complexity (A VL500A for example has 16 flags). There is also glass type mechanical dimmers seen in Vari-Lites. This, however, also causes a drop in optical quality despite being much better then a flag system (the VL2500 has less output vs the VL2000 because it uses a glass system despite being the same fixtures). There is really no such thing as an electrical shutter since halogens and incandescents can't strobe. They are instead just simply considered dimable.
Also, shutters are used for other things besides dimming lights. In ellipsoidals (lekos), they are used for framing (commonly known as Framing Shutters because of this) out the light. Some moving lights have these types of shutters in them as well.
Otherwise, good information guys.
Edit: Halogens are also used in just about every stage light. Opti Pars and Par Xs all use halogens for example. The DJ Spot 250 has a shutter/s so it can strobe, not for dimming. They might have not included a built in dimmer though, so the lamp might not dim and instead dims via the shutter/s. Trackspots, for example, actually dim the lamp when you dim them. They also have a shutter so they can strobe. They use halogen lamps as well. In fact, the only place incandescents are still used today are homes/living spaces since you can handle the lamp with your hands without shortening lamp life. They are also safe since they don't explode (I have seen halogen lamps explode before).
Much better when reading with a fresh set of eyes, amazing what one can miss. Lol.