A black surface does indeed radiate heat better!!!!
I think the main reason the pros anodize black, is it simply looks more professional, and keeps the parts looking good while they sit on the shelf. While they may claim its to radiate heat better (which it does) to make it sound more "engineered", I think that is simply an "added bonus". It just simply looks more professional, and it does add corrosion and discoloration prevention. If Coherent, Ophir etc. didnt anodize their heads, the time spent on the shelf before they are sold is enough to make bare aluminum look "dingy", and not a very presentable product. Yes, bare aluminum can become discolored, especially if its a dusty environment. It happens all the time with parts at work, and we have resorted to chemical brighteners to make them look "new" again if they have been on the shelf long enough. If its been a LOOOONG time, and depending on the alloy, aluminum oxide can actually start to be visible as a white dusty looking surface. Bottom line, IMHO , I think its more of a manufacturing/sales decision more than an engineered solution to a thermal issue.