IBL is Image Based Lighting, available in Poser 6 and 7.

In the picture, you have the same model, with the same skin shader, in two different lighting environments. The IBL is from Danae's Manhattan package. Complex lighting system comes from Orion's London set.

Neither is better or worse, they're just different and used for different purposes.

Generally, in IBL good skin textures look better, but bad look terrible :)