Two reasons why I think this might not actually happen:
1) To remove glazing, the slots need to take off appreciable amounts of material - some posts I found indicate that 120 grit sandpaper is recommended to remove glazed material. However, if this was the case, the slots would be doing this ALL THE TIME and the pads would last only a short while before being worn out. Since pad life is not excessively shortened by the use of slotted rotors, I would think that the slots do little, if any, "cutting" of the pad.
2) A glazed pad, in practice, is pretty much ruined until repaired/replaced, no?
Glazed pads are ruined. Glazed pads are caused by excessive heat separating the pad material mixture and then, when cooled, the materials cool in a crystalline structure. This is much more common during the beginning of pad life, when someone ignores the bedding in phase and stresses pads under a hard work cycle.
The only recommendation I give for glazed pads is replace them. Yes, the temps may have only glazed part of the pads, but the glazing could be uneven and it could go much deeper. You can sand the surface, but your pads would not be the same because the rest of the material also reached at least nearly critical temperatures.
Slotted rotors will not prevent glazing unless whoever meant that the slightly lower temps might prevent onset, but even then it's a minimal effect. Slotted and drilled rotors heat up more quickly and the also cool more quickly. Less materials = less heat capacity and in the end you're still trying to dissipate the same amount of energy (except for the minimal difference in unsprung mass of a drilled or slotted rotor v.s. a solid blank, all other things being equal).
For road use, I highly recommend getting some "Brembo Blanks" aka Brembo OEM rotors. Strong, thick, quality metal that provides an excellent friction surface for stopping. For race use, obviously, pair up a good, quality blank rotor and the correct temperature pads. Slotted rotors are for looks only, total cooling surface area and airflow is not increased much at all and using the wrong brake pads (IE super high performance pads for street use and vice versa) will actually decrease braking ability since the friction material coefficent of friction is dependent on temperature and if you're not in the sweet spot, your bite quality and general responsiveness actually gets worse. With the advent of new pad materials in the last 20 years, drilling and slotting rotors have become something that is not only unneeded, it is now decreasing performance just for show.
This of course only applies to street cars with iron rotors and Dot 3/4 fluid. F1 for example heavily favors solid rotor surfaces (As with as does LMP1 cars and NASCAR). The GT class cars favor rotors with 6 dimples in them.
For the original discussion
Solid surface>>>>>>Slotted>>Drilled
I'll try to find the quote where Ferrari said the put drilled or slotted rotors on their street cars and run blank rotors on F1 cars because customers preferred the looks of those rotors, not because it improves performance. It was in a C&D or R&T sometime.
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