Yeah, it's something you see in cell phone batts (which are also NiCd or NiMH). There's a difference between the car charger and the wall charger you get with a cell. The wall charger takes longer to charge because it uses fewer amps. The car charger is usually called a quick charger, and it feeds more amps to the batts than the wall brick. If you use the quick charger as your main charger, it'll eventually give the batteries memory, but in the short run that burst of power you gave the batteries will dump faster than if you trickle em. I think if I wanted to use an analogy, the closest would be an oven. Cooking something for an hour at 250F is quite different from cooking it for 30 minutes at 500.
Incidentally, some quick chargers have a trickle feature. My cheapie Duratrax charger has it. It'll peak charge for 20-30 minutes at 4.5A, then trickle at ~300mA. I can plug in a battery to peak charge it, or leave it on for 4 hours. The trickle allows the burst of power to disseminate evenly through the cells.