Many web sites do comparison between Android-based tablets and iPad, but unfortunately almost none of them mention about one important thing: upward/downward binary-compatibility.
What does that mean? OK, we now that a software or an application is actually stored in file. On desktop operating systems (Windows, Mac, Linux etc.), these files are executable on their respective O/S, but only for specific machine.
iPad (or iPhone) Applications are actually binary applications similar the ones we find on Windows or Mac in that they contain machine instructions directly instruct each step to be taken by CPU. The instruction set is specific to the CPU it is built on (for example, iPad app cannot run on Windows or Linux, unless we have an emulator to translate the machine code on-the-fly).
The mechanism of running application is Android is slightly different. Although Android O/S kernel is based on Linux, its applications run on top of a Java virtual machine called "Dalvik". It specifies its own instruction set, outside the platform it runs on (Linux). It acts as a new realm in a realm. The benefit is that we can run Android application on any machine we like (as long as we have the Android O/S compiled and run on the specific CPU). theoritically, an application built for Android running on MIPS CPU can also run on Intel CPU so on.
Why it is important? because developers are no more tied to develop an application specific to a CPU. They can just develop once and it will run on various machines.