Successful managers vs effective managers

Trying to think a bit more clearly about the difference between effective managers (i.e., ones who solve problems) and successful managers (i.e., ones who get promoted), I find myself reading a 1988 paper by Professor Fred Luthans, who was/is George Holmes Distinguished Professor of Management at the University of Nebraska at Lincoln.

Professor Luthans 'found that communication and human resource management activities made by far the largest relative contribution to real managers' effectiveness and that traditional management and - especially - networking made by far the least relative contribution'.

By contrast, 'networking activity had by far the strongest relative relationship to success'.

And in summary, less than a tenth of managers made the top third of both 'successful' and 'effective' groups - which is what you would expect if there were no connection between the two.

Scary? Anyone have any ideas about how valid this finding is? Or how it is possible?

[Update - a quick email exchange with Professor Luthans confirms that, in his view, this is still the position.]

[Further update - I show this to various colleagues. They laugh. Basically, our bosses are blagging their way to the top (for non-London readers, that means getting to the top by less than legitimate means.) And no one is even faintly surprised.]