Despite what many sites say, I do not think that the iPad is innovative, the best in its field, or even responsible for its "copycats". If you think about it, tablet PCs have been around for ages but only recently were they popularized. Many would say that the iPad "lead the way," but I would argue differently.
See, here's how I think it goes. There are Apple zombies. Yes, there are. There are the people that will sell their iDevice 1 six months after buying it to buy an iDevice 2, losing hundreds of dollars in the process. It's not even the product that drives most of these people because I bet dollars to donuts that if you asked most of them why they're upgrading, few would give you a reason, let alone answer the question of "Is it worth it?" So what drives them? Well, it's Apple fanism. Apple tells them that a product is good/better, and they believe it. When looking at this from Apple's standpoint, this is insane marketing. They could release the "iPhone 4c", which just had a colored shell, and people would still drop hundreds of dollars to have one, which is very good from the view of a company.
But anyway, we've got all these people that will buy almost any Apple product because they own a different Apple product. So when Apple releases a new type of product, say the iPad, people flock to the stores to buy one, even if it's unoriginal on two fronts (a tablet PC and a giant iPod Touch). So what does this mean? It means that at this point, Apple has got the tablet market in its pocket because even people that don't follow Apple will hear about the iPad and then consider it. Of course, other companies want in on the action and start releasing their "imitators," a term which denotes that they are trying to be iPads. But are they really? I've yet to see a pattern of tablets striving to be like the iPad, other than just by being a tablet.
This begs the real question: does the increase in attention on tablets resulting from the iPad = copying the iPad? I would say no. I believe that tablets were just naturally coming, since we've more and more been making the link between mobile phone and desktop computers. Unfortunately though, especially after the lack of boom from netbooks (or lack of a big boom, rather), most companies were probably scared to try to dance into the tablet territory. Not the mention the fact that Android -the only OS really fitted for a tablet- had not yet stepped into the tablet ring, mostly because tablets had not existed yet. (Kind of a "chicken or egg" thing.) So in order to make the first large step, a company like Apple was needed to break the ice and introduce tablets to a market and give tablets a nice face. After the iPad's release, people were no longer skeptical, it was proven. Tablets are awesome. This opened the door for other tablets -not iPad imitators, just other tablets.
tl;dr: Apple's zombie users means that anything they release will sell, including that of tablets. The iPad "imitators" were not imitating the iPad, they only used the attention that came from the Apple zombies to tablets in general.
That's just my unpolished theory. If you disagree and plan on flaming me, stop. What part of "unpolished" and "theory" do you not understand?