This isn't necessarily true and varies person to person. I live in the south as well and have oily skin/hair to boot. Suffice to say I HAVE to wash my hair once a day or I wouldn't look appropriate in public.
+1 on not washing your hair every day. I've tried tons of shampoos, and paid all sorts of prices for them. Only a few have seemed to truly be gentle on my hair. But, it seems that almost every time I wash my hair, my scalp and hair gets dried out, causing my hair to be poofy and stick out. Even, when I wash in only cold water.
Unfortunately, I live in the south, and my job requires me to do hard work outside inside hot auto shops. So, during the week I was my hair every day, don't on the weekends.