Yes it is. I was talking with someone earlier today who said he knew OpenGL, and said it looked wrong, so I figured he knew what he was talking about. I suppose not ^_^;
I suppose I should have googled this first. There seems to be a pretty good explanation of how the triangulation of quads effects the resulting gradient.
To reference this image here
http://cs.wellesley.edu/~cs307/readings/ColorInterpolationQuads.pngI was expecting the bottom right result, but opengl generates the top left one.