Huge difference...
If I pay at the end of 2017 my insurance premiums for the entirety of 2018, the insurance company provides me with the promised insurance for all of 2018.
On the other hand, if I buy EAP and FSD at the end of 2017, there is absolutely no promise about what will be delivered in 2018 or when. And Tesla is incentivized to release something half-assed during 2018, before it is actually ready/tested, since it feels like it has to deliver something.
People who buy EAP/FSD only have extremely unreliable information (ie what Tesla states publicly) about what the software will do and when it will be delivered. Not so with prepaid insurance.
It's a gamble evidently many are willing to take. Personally, I try not to buy something based on what it "might" do in the future. Only what it does do today. (Except for stock purchases I suppose.). I didn't buy EAP nor FSD until I feel it is ready. That was my "choice". Just like everyone else.