To put it shortly, it is a mobile OS made for mobile devices. This will increase in significance in the near future as mobile computing becomes the dominant activity for many computer users, if not most, and Windows is currently leveling out and excruciatingly slow when it comes to adapting to changes in mobile technology as it is taking a while for them to forget the industry rules and standards that they helped build.
Thirdly, although netbooks can claim the advantage of running the kinds of applications their desktop/laptop cousins can and therefore offer some continuity and compatibility for users, this actually constrains the functionality of the device. In a nutshell, all netbooks are doing is offering more of just the same in a smaller and cheaper (and you can say less well-built) package. It is therefore reliant on the traditional monolithic software developers to write applications for desktop and laptop machines which it can then use for its functionality. The iPad application is rather different in this way.
Although there are some overlaps between desktop/laptop software such as iWork, Google Earth and so on, generally speaking the apps in the App Store are original and have been written specifically for mobile devices and generally, are higher in quality compared to other apps offered out on the web. This is important for at least two reasons: they are written for mobile computing and it is an ever-changing creative landscape. Applications written by developers for the iPad are designed for the needs of hand-held computing and can take account of dimensions such as device location, battery drain and screen size. Mobile computing creates new demands for devices and software and the iPad OS is written for that purpose, netbooks do not compensate for and account of this situation in a resembling way.