Marmol throws in the mid 90's no where near the velocity of Rodriguez. If I were a betting man, I'd bet that Marmol's success is directly tied to one pitch,his slider. Rodriguez actually has a nice breaking ball (Slider/curve/slurve... whatever) to go along with the 98-100 heater.
The problem with HRod's heater is that if he takes some of the velocity off to gain some control he's going to be very hittable but much more accurate. I'm just glad he's starting to get it together but I don't trust him in any game that's close.