The reason why iOS is designed differently from OS XSeptember 20th, 2011
Someone in the jailbreaking community has created a theme called Lion Ultimatum, bringing the look-and-feel of the OS X Lion desktop to iPhone and iPod touch. Normally you would expect a theme to change just the background image and icons, but Lion Ultimatum gives you usable menu, draggable window, mission control, stacks, launchpad, scrollable dock and dashboard.
Lion Ultimatum is available for jailbroken iPhones and iPod touch only. Not sure if you want your phone to operate this way. The theme also shows why Apple has a different interface design for iOS to fit a smaller touchscreen.