At the same quality level, it's hard for anyone to undercut apple on price on iPad, unless you do a 0-margin product (google, amazon).
In contrast, iPhone has lots of margin, so it's relatively easy for other players.
The margins are estimated to be ~37% - ~50% depending on the model. http://www.isuppli.com/Teardowns/News/Pages/New-iPad-32-GB-4...
Those estimated margins aren't as high as iPhone (http://www.isuppli.com/Teardowns/News/Pages/iPhone5-Carries-...) but are still pretty damn good :-)
37% for apple might only be 25% for any other competitor, because apples supply chain is so streamlined and locked down. So it's hard to compete with the base iPad on price.
At 50%, you are right, there could be room to undercut, but that's only the high-end iPad (eg 64gb) which isn't where the volume is.
iPhone margins are much better, and thus leave more room for others to undercut or offer feature parity.
Hmmm... I might be wrong, but I thought they have HUGE margins. You know, like 40%? Keep in mind that the most popular iPad, 32GB 4G is $729. The $499 model is not the most popular one (at least according to the analysts).
For some reason I find that hard to believe: that the most expensive iPad is the most popular one as opposed to to the 16 GB WIFI only version.
Arguably, early adopters are different than "late"-adopters, but still... The "analysis" that I remember was for iPad 3, and it was a few months after the launch.