The poll I saw (Pew, maybe?) only counted the white Protestant vote. Given that blacks are overwhelmingly Protestant and voted overwhelmingly for Obama, I don't think they could have been factored into the overall Protestant vote. Maybe so, because of the difference in population percentage, but if you have some stats, it would be interesting to take a look at them.
Stats for what, the overall Protestant vote in America since 1928 that includes blacks in the total, it always does. The 46% of Protestants that voted for Obama in 2008 includes the black voters.
Blacks are always included in the Protestant vote unless a study is specifically separating out for race.
The Protestants (including the black Protestants as part of the total) have only voted Democrat in 1932, 1936 and 1964 going back to before 1928.
People don’t realize that FDR was depending on massive Catholic support in 1940 and 1944, Protestants were voting Republican again after having strayed in 32 and 36.