Yup. The quad cable has a small but definite noise advantage over simple 2-conductor (shielded twisted pair) cable, due to the way the magnetic fields around each conductor interact. This is *much* more important for mic level signals than for line level signals: mic level signals need all the noise rejection help they can get, especially if you have a noisy EMI/RFI environment (dimmers, flourescent lights, computers....).
I'm not convinced that quad offers a big enough advantage for line level signals to say "use it for everything": quad still carries a pretty high price premium. I personally use both, and tend to reserve the quad for mic cables only. But if you can afford it, or if you only want to stock one roll of cable, then quad will give you the best noise performance for mic signals...
One thing to add: the capacitance of the quad cables is usually significantly higher than regular 2-conductor. This isn't an issue with mics, because their source impedance is so low (a few tens to a few hundreds of ohms). Ditto for line-level use, where the drivers will always have very low impedances. But if you use quad with a high-impedance source (your Telecaster, for example, or your old Shure Uniball high-Z mic), the higher capacitance can and will roll off your highs: the longer the cable, the more profound the effect. So if you decide to have only one roll of cable, and you want it to be quad, _don't_ use it for building guitar cables...
For that sort of high impedance, single-ended use, you really want the specialized low-capacitance single-conductor cable that is optimized for that use. One size does not fit all!
