New 4200mAh cell debuts this mounth

[Batfish]

The better way to put this may be: the voltage drop will be less under load, therefore operating voltage will likely be higher when using batteries in parallel. Initial voltage will NOT be higher.
For example (I know these numbers aren't perfect, so bear with me):
If you have a single 6-cell 3300 pack running at 7.2v and you stab the throttle - the voltage may drop to 6v during the immediate accelleration, then rise back up to near 7.2v. You've got 6 cells pushing the requested power.
If you have two 6-cell 3300 packs wired in parallel at 7.2v and 6600mah and you stab the throttle, the voltage may only drop to 6.5 volts, which means you'll get better power. Here you have 12 cells pushing the requested power, so they don't have to work as hard as just 6.

Of course, then you have to figure in the weight gain from parallel packs. This is why you almost never hear of nimh running in parallel; the weight will probably cancel out the benefits. However, the lipo world of light weight cells now has made parallel connections a reality, so we're hearing a lot more about it now.

Hope that helps :)