People want iPads, not tablets. People don't even know what "tablets" are. Apple have defined a new market, most people buying iPads aren't really sure why they want them yet. It will be impossible for the competition to win over mindshare until they have something *better* than the iPad has. Price will not convince many because as said, people don't want tablets, they want iPads.
This will probably change. But it will take a few years yet IMO. Think about how long it took for people to know why they wanted a PC. This is different (people understand why they want a computer nowadays), but it will still take time.