I used to have that same opinion actually but then I had a conversation with someone who has been in software development for several years. My feelings haven't changed, mind you, but I'm not nearly as stubborn about apps that do this.

Consider: Not all companies running a given software package have a DBA full or part-time. If they don't, then the application administrator must be able to create new SQL logins through the application itself. To do this requires sysadmin rights.

Check out http://databasejournal.com/features/mssql/article.php/1473011 for a good discussion on why GreatPlains decided to use the sa account in its application. Yes, it can be turned off. However, it increases workload for the DBA who now has to create SQL accounts by hand.