Whether you plunked down $699 for a brand-new iPad or got an old iPhone 4S for free on special, it's your device. Too bad Apple doesn't think so, as the company hides your file system from you, making it difficult to attach documents to email and impossible to browse the folders.
On Android, you can attach any type of file you want to your emails, whether you compose them in Gmail or a third-party app like K-9 Mail. However, in iOS, you can only attach photos and videos from directly within the email app. If you want to send an Office doc, PowerPoint presentation or some other file type, you'll need to send them by using the Share function of another app, such as iWork.
When you connect your Android device to a PC, you can browse its file system as you would with any USB flash drive. When you plug an iPhone into your computer, you'll only see the folder with the photos, and nothing more.