edit: Care to explain the down votes? It's too early to make such proclamations. It took a while for the cellphone market to catch up with Apple, why should we expect the tablet market to be any different?
True, but the tablet market is in one important aspect different from the phone market, in that the distribution channels are vastly different. Many who buy a new phone just take what the carriers are shoving in their sales channel.
In the best case scenario the iPad could play out more like the iPod: year after year there were prominent iPod-killers like the Zune and cheap knockoffs and year after year Apple dominated the market.
iPhone didn't immediately command a large percentage of the market, the iPad does. This is much closer to the iPod situation where many companies tried to match it but failed.
For one thing it was Apple's exclusivity with AT&T that opened the door for Verizon to push Android which played a vital role in its success. Things are a bit different with the iPad being that it's offered in both CDMA and GSM and the wifi-only model is, by far, the most popular.
It's also important to note there's really only one successful competitor to the iPhone -- Android. WebOS is dead, RIM is on the ropes, HTC, Samsung, Motorola, LG, etc didn't catch up as much as they let Google catch-up and they rode their success. (my point being we can't under estimate the difficulty in trying to compete toe-to-toe with iOS as only one company has done it successfully to date)
edit: Care to explain the down votes? It's too early to make such proclamations. It took a while for the cellphone market to catch up with Apple, why should we expect the tablet market to be any different?