These days more than ever the hardware only makes one difference - what inputs are available. There are a few other minor considerations like which APIs are enabled for developers, but really the only significant factor is how you can get information into the machine. Everything else like CPU speed, RAM, storage, etc are problems that, for the ordinary user at least, are solved.
The iPad is designed to make it easy to enter spacial information (where you're pressing on the screen) compared to a mouse or a keyboard. That's why it'll make a great reader, web browsing tool, and gaming device, but a relatively poor word processor or data entry device. A netbook on the other hand isn't really optimised for information entry at all. The keyboard isn't as good as a laptop, it's harder to operate a touchscreen on one than a tablet, and there's usually a pretty rubbish trackpad. Netbooks are a great compromise but they're not going to win in the long term when we can make laptops fold up smaller (somehow!).
In the future there will be a place for tablet PCs while there won't be for netbooks. I'm sure Bill is right that for now MSFT's interest lies in the netbook, but looking to the longer term he's dead wrong.