"Rule #30: It is mainly the incompetent that don't like to show off their work."
Madden's remark is based on the specific environment he was involved in (NASA engineering); if you're surrounded by people who are good at their jobs and who know how to criticise constructively then there aren't many reasons to hide what you're doing other than it being a bit rubbish. I don't entirely agree with the idea that people who don't show things off are necessarily incompetent, especially if showing off your work means putting it under general public scrutiny (who can be very nasty), but there's a huge amount of value to be gained in getting feedback from your peers as early as possible.
 http://www.nasa.gov/pdf/293253main_62682main_jerry_madden_fo... (Non-PDF version: http://www.altisinc.com/resources/rules/ )
The all important point is a constructive team that knows their job. But especially in space project related development, you may be surprised to find managers who don't know much about software.
Or, they don't show it off for fear of the ungrateful comments that projects tend to get because they don't implement some feature, or there's some obscure bug that the author doesn't consider important, or haven't updated it in a while, and so on.