iOS 4.2 and 4.3 introduced 'multi-tasking'. But it's not multi-tasking as the PC world knows it - more 'task swapping', where programs (apps) can be switched in and out of the iPad's memory (RAM).
The term "multitasking" has been loosely and interchangeably used to refer to various methods of time-sharing various programs on the CPU, so statements like "there is no multitasking on iPad" need to be qualified and taken in context.
There are several types of multitasking and they all involve some level of task switching - essentially because each CPU can execute one task at a time (although a CPU executing millions of tasks in one second can make it look like it's doing several things simultaneously.)
For example, in multi-programming mode, there is only one task running on the CPU until a triggering event (whether user or computer-triggered) causes the task to be swapped out of CPU, which is what you see on iOS. In time-shared multitasking (although the term "time-shared" itself is obsolete), several programs appear to run simultaneously to our human perception, because the tasks are time-sliced within the CPU in rapid succession.