Anyone heard of a regular American Buttercream recipe that calls for a LITTLE cake flour, which I believe, lessens the sweetness of the buttercream?

Plenty of variations around ... Try
Buttercream Icing [Crusting]
1 ½ c shortening ...... ½ c cake flour
2 to 3 lb icing sugar .. ¾ c warm water
1 ts vanilla ................ 1 ts almond extract
1 ts fine salt
Beat shortening and flour.
Mix water, flavour and salt then add alternately with the sugar.
Continue on low speed.

Buttercream Icing - Wilton Variation
2 c shortening ........ ½ c water
2 ts vanilla flavour .. 2 ts butter flavour
1 ts almond flavour . 1 ts popcorn salt
¼ c cornstarch ........ 8 c icing sugar
Beat shortening and liquids 3-5 min then add remainder.
Mix on low .

Bakery Icing
2 c Butter ........ 4 c sugar
2 ts vanilla ...... 1 ½ c Shortening
¼ c cornstarch in 2 c warm milk or water
Cream butter, shortening , sugar and vanilla.
Dissolve cornstarch into liquid - add to butter.
Beat until creamy.

I want to try this one pretty soon:

http://cakecentral.com/recipe/julies-less-sweet-buttercream-frosting

Here's a recipe from my cousin who has made cakes for 30+ years. She lives in a very hot/humid southern state and says this holds up very well.

Ricki's Crusting Buttercream (high-heat, high-humidity)
1 cup + 4 TBSP water
2 cup Crisco (use high-ratio shortening if you have it)
½ tsp popcorn salt
1 tsp butter flavor
1 tsp almond extract
2 tsp clear vanilla
8 tsp meringue powder
4 TBSP cake flour
1 cup corn starch
4 lb. C&H sifted powdered sugar
The recipe above is a double batch. Any leftover icing will be ok in the fridge/freezer.