The abort system for the Dragon capsule provides 4.5G of acceleration (human dragon space flight will not reach 5G, don't mix in cargo launches, irrc SpaceX said that the nominal max acc. for human flight will be below 3G similar to an STS launch) and it does kinda abort side ways, as soon as it clears the main rocket it tilts and gets the heck out of the way because it's quit important to be as far away from the rocket as possible in case it explodes (also to prevent any chance of rocket derby catching with the capsule during decent) and out-running it upwards isn't a possible in the long run.

If the point is to abort, you can't rely on the engines being throttled down to the accel limit -- you have to be able to successfully get out of any reasonable scenario and the engines running away does not seem unreasonable. (I don't know exactly what the abort requirements are, but the point is just that it's not easy.)

Also, during an abort scenario, the aero drag is pushing Dragon back onto the launch vehicle, so you actually need more thrust to overcome that, too. (Although that obviously depends very strongly on the dynamic pressure at which you abort.)