From the iPhone Human Interface Guidelines
Although the ultimate purpose of an application is to enable a task, even if that task is playing a game, the importance of an application’s appearance should not be underestimated. This is because appearance has a strong impact on functionality: An application that appears cluttered or illogical is hard to understand and use.
See also In defense of eye candy
We’ve all seen arguments in the design community that dismiss the role of beauty in visual interfaces, insisting that good designers base their choices strictly on matters of branding or basic design principles. Lost in these discussions is an understanding of the powerful role aesthetics play in shaping how we come to know, feel, and respond.
Truth may not be beauty but beauty does help truth get recognized.