The plastic tipped bullets such as Hornady SST's and Nosler Ballistic Tips are really HP bullets with a plastic tip for better aerodynamics. When they hit game the plastic tip is driven into the HP and aid's in expansion.
Many target bullets as well as the Berger VLD Hunting bullets have a tiny opening in the tip. These are they type Art is referring to. They weren't initially made as a hunting bullet or intended as a true HP. But many hunters tried them and found that they work. Bullet makers responded by tweaking the design for more reliable expansion and now market a version of the as a hunting bullet. I still wouldn't recommend a bullet designed as a target bullet for hunting, although many have tried it and found it to work.
This is a photo of Hornady's version including a cross section. They all work very much the same. Notice, this bullet is not recommended for hunting.
http://www.hornady.com/store/30-Cal-.308-168-gr-BTHP/