Past presidents have been accused of appointing secretaries of commerce with the intent of having them funnel money to and from their major financial backers. This report by the PBS show Frontline discusses that topic.
Under the old Post Office Department structure, before the quasi-independent U.S. Postal Service was created in 1971, presidents often appointed their campaign managers as Postmaster General, which was then a Cabinet position. Why was that?
Before 1971, the president appointed many of the local postmasters. Many observers, including Bill Schneider in this CNN report dating back to 1997, describe that as an opportunity for a president to reward political allies around the country.
Now, postmasters are chosen by the civil service merit system and, in the opinion of some of those observers, the Commerce Department has taken over the patronage function.
By selecting, if belatedly, a member of the opposition party for secretary of commerce, President Obama seems to be signaling that he does not intend to use the department that way.