Acrylic painters use glazing (layering) to achieve the blending effect instead of actually blending the paint due to the fast drying time. While you can use retarders to slow down the drying time and actually blend acrylic paint, it is better not to use acrylic paints like oil based paints.
Here is an excellent article on using acrylic paints for figure painting:
http://www.ttfxmedia.com/vallejo/cgi-bin/_modelis.asp?p1=ing&p2=modelcolortecnicas
and another article using arcrylics for figure painting:
http://alphaimagemodelworkshop.com/Web%20pages/Article%20pages/german_ss_in_greatcoat.htm
To me, it seems like even the acrylic painters will resort to using oils for the faces so they can blend the paint. It boils down to two different schools of figure painting when it comes to acrylics and oils.