http://blog.atebits.com/2008/12/settings-are-in-the-settings-app/

Take the Weather app for example. This offers “configuration options” on the backside to manage different cities. Likewise, the Stocks app flips over to allow configuration of your stocks.

Mail on the other hand makes you manage your accounts and settings in the Settings app itself. This makes sense – you are much more likely to change what stocks you watch or what cities you’d like to check the weather for than make a new email account or change the minimum font size. The only real difference between a “setting” and a “configuration” is how often they change.

There are two problems with the way Settings work on iPhone. The first is a technical problem, the second is a developer problem. The technical problem is that third party applications cannot execute their own code in the Setting app itself. This leaves them crippled, and it’s the only reason why I didn’t include the account management features of Tweetie in Settings.

The second problem is that many developers have chosen to eschew the Settings app altogether, deciding instead to put all their settings in the app itself. In cases where where executing code is required, this is forgivable. In other cases it is not, and just sets bad precedent and teaches users the wrong way of doing things.