For disclosure - I have (and like) a Windows desktop PC, a MacBook aluminum 2.4GHz, an iPod touch, a Nexus One, a Kindle, and an HP EliteBook for work, among other stuff. I am willing to shop around and make disinterested comparisons. I am planning to buy an iPad, and when I do, I am likely to sell the Kindle, Apple TV and MacBook.
iPad rivals are already behind.
Forgetting about size, weight, cameras, memory, processor speeds, etc...those features are transient as the hardware refreshes every year...
1. Even after 3 years, no one seems to have been able to replicate the iPhone touch UI. The competitions' UIs are sluggish and choppy/laggy. Their screens and/or OSes don't do multitouch well. Some have shown they know how to do it right, but the hardware doesn't seem to want to cooperate.
My Nexus One's touch UI is very nice. And it does multitouch, but not as well/universally (it was held out for a long time over fear of lawsuits). But I don't really miss it ... maybe just what I'm used to. The Nexus One is also much thinner than an iPhone, closer to the thickness of a touch, and the better specs are noticeable in use. Of course, the 4g iPhone will seesaw back ahead technologically.
2. The app store is a monster. It has a 3 year head start in development. 150,000+ apps, vs. 30,000 from the next closest competitor, Android.
At some point, who cares? 30,000 is a lot. 150,000 is a lot more, but how many of the additional apps are things you'd care about, and how many duplicate functionality or are basically RSS feeds or other low-value items? I work for a company that develops software for consumers, and we rolled out iPhone apps last year; this year, we're looking at iPhone, iPad and Android with roughly equal focus. We are about to pay a third party $90k or so to port a successful iPhone app to Android. In terms of quality apps, the gap is not that huge and is going to shrink as many companies support both equally to hedge their bets.
3. The Apple data cloud seems to be growing. The more people are tied into MobileMe, via their iPhones, their Macs, and now their iPads, the less reason they have to stray. Any device that Apple makes which works within their cloud has a compelling feature set already built in, made even more so if you already own their other products.
The Apple data cloud may be growing, but the google data cloud is enormous.
There is no real competitor for the iPad now, and until a real competitor actually exists and can be purchased, it's pointless to sit around waiting for it, or comparing the iPad against imaginary rivals. There is nothing like the iPad on the market today, not to say it's for everybody, but you either want one or you don't. You can't directly weigh it against anything else.
That said, I think there is a big opening for an HTC/Google rival to emerge relatively quickly and for a wide range of Android-powered rivals to emerge in the next year, and I hope they do - competition is always better than no competition.