You are comparing this device to other devices that honestly lacked the kind of popular appeal that modern tablets do. Sure, it was running a great OS for the time but that OS did not have the kind of app ecosystem that the iPad does. That ecosystem is pretty critical to the popularity of the device.
and yes, check the UID, I was on line in 2000, quite a bit before that actually, and frankly the web was not the most interesting place for the mainstream. Sure, for hard core geeks it was great but that was not going to be enough to kick off a serious change in the way normal people interacted with technology.
When the iPad came out we already had a really rich web experience available, people had already started supporting mobile safari extensively thanks to the iPhone and there was an existing ecosystem of high quality apps available and plenty of companies and engineers available who's goal was to grow that eco system. This device had none of that and without that it was not going to be successful. Honestly I am not so sure that the iPad would have even managed to take off if it were not for the iPhone that came before it, to pull it off when all wireless bandwidth was slow and expensive and the web was a mostly static place to read news and there were no social networks to speak of.... most people would not have use for such a device.
Plus, we still don't know what it would have cost, which is another huge barrier to adoption.