Abs are a muscle group :P
They need the same amount of exercise and rest as any part of the body, there's a myth that abs recovers faster since it's a part of your core and this is DEFINITELY NOT TRUE.
Mainly because the abs will SEEM to recover faster cause after a while abs won't get sore as much. But then honestly out of any body exercise out there abs are the ONLY muscle people are happy with working without weights 90% of the times.
Without increased resistance and with a set number of reps or sets of COURSE your abs will feel like they recover faster cause you've settled on a plateau level of resistance and training program.
if you want REAL results in working out your abs and feeling sore add weights and try cable crunches with 50 pounds of resistance
You'll feel them hurt MORE and LONGER than your chest or back workouts
If you compare your ab workout to say your chest workout for the normal guy, most normal guys will try to lift more weights every couple weeks without changing their number of reps too much. but with abs they'll settle on 100 crunches, 100 leg raises, 100 swiss ball crunches without ever adding weights and call it a day. With the only added weight is usually extra body weight from muscle or food and water you had that day.