This week's book giveaway is in the Mac OS forum. We're giving away four copies of a choice of "Take Control of Upgrading to Yosemite" or "Take Control of Automating Your Mac" and have Joe Kissell on-line! See this thread for details.
It may have to do with the preference of the developers as well. But using vendor specific annotations over a config files can limit the portability of the application to a different vendor. If for example JPA annotations can be used as they are widely implemented by the vendors as it is the standard for the Java persistence.