I'm not sure if it's usually required. When I applied for my E visa around May, it was mandatory, so I bought it. I usually get travel insurance anyway.
I heard that the requirement was later scrapped, but I don't have any source to verify that.
Either way, when I got there, the customs guy didn't check. Just looked at my passport, looked at me suspiciously, paused as if disconcerted by something, then stamped the passport and off I went to luggage retrieval.