I think the iPad is akin to iPods. Nobody knew they wanted an MP3 player until iPods came out. Nobody knew they wanted a tablet until iPads came out. Competitors are STILL coming out with competition to the iPod, but can you name more than a handful of standouts, and can you name any that have sold a lot of units?
I think in the smartphone world, people are buying what's a) free, b) available on their carrier, and c) the closest they can get to an iPhone. This is not true for everyone, of course. There are plenty of people out there who don't want iPhones, but there are also plenty of people out there who bought Android phones and still want iPhones--they just couldn't get them and weren't willing to switch carriers to do it.
iPads, much like iPods, are not in the same situation. You are not tied to a carrier or contract. You are not being sold on something by an 18 year old at the cell phone store who has his/her own agenda for making commissions. You are (hopefully) simply doing your research, shopping for your tablet, and buying the one you want. In that situation, the one most people want is the iPad. If these Android tablets were in any way desirable, they'd be selling better. But it just goes to show that despite Android being more widespread on cell phones, it is not necessarily the OS of choice, but rather the one being more or less forced on people.
In light of recent product rumors, releases, sales numbers, and product announcements, I truly have a feeling that we are about to see Apple execute at a level we have not yet seen. I feel like they are getting ready for a huge push in several of their markets. Because of this, I'm glad I have spent the last year slowly migrating my technology over to Apple stuff. My house is getting more and more Apple-y by the day. And whenever I see a new Android tablet review or product release, I am even happier that I picked the iPad.