It's true, unless your trying to build big muscles, it's better to do many reps and less weight. Burns more fat and tones the muscle.

I recommend, for abs, not to use weight machines. They are very limited in what muscles they target and I find I can easily hurt my back doing them.
Best thing to use: Pilates! Seriously it is amazing for an ab work out, and incorporates stretching into it. I honestly just use Pilates for my strength training instead of weights. Tones the body wonderfully! (course I haven't been doing it for months now, need to find the motivation to work out again LOL)