Tooltips are not typically seen in iPhone apps. The screenshot was from the hipmunk web application. Perhaps hipmunk assumes that anyone using their iPhone app

Tooltips are not typically seen in iPhone apps. The screenshot was from the hipmunk web application. Perhaps hipmunk assumes that anyone using their iPhone app is already familiar with the web app and shouldn't be treated as a novice user. Or perhaps they have so much confidence that their agony ranking is what you want that they don't feel compelled to explain it. ;)