I'm no fan of Apple (use a PC and a windows smartphone) and I find most praise of Apple tends to be rather over the top, but there is no doubt that they do the best tablet, especially for less tech-competent users. Their strict quality control over both the iOS releases and apps ensures a generally good user experience and overall they have a better ease of use than the Android options. Although Android is improving quickly it can still be a little all over the place and occasionally it's apps are unstable.

I would advise getting an iPad 2. Although it is not quite as swanky as the latest version it will be more than enough for your parents (I'm still happily using an iPad 1). The big difference is price. From the NZ Apple site you can buy the latest iPad from NZ$ 729, while you can get the iPad2 from NZ$ 579.

I would sound a note of caution about tablet's in general. Although older less competent users often find them better and easier to use for the majority of their computer needs, there are some tasks (such as printing) for which they are ill-suited. Sometimes access to a laptop or desktop is still needed.