"To me this seems like a definite pre-emptive action to protect themselves if Poloniex either negligently or maliciously loses your money."
Agreed, but as I'm guessing you already know, this is a pretty standard piece of boilerplate legalese, at least in the US. You agree to this with a ton of other contracts - utilities, large purchases, etc.
The first 5 out of 6 things you listed above also apply to Coinbase/GDAX. Particularly the truly awful service. I'm avoiding both of these locations as much as humanly possible.
Thanks for the recap.
I would not be surprised I think sometimes they recycle these things and possibly don't even check themselves. That said this is a conscious decision on their part to change.
As for Coinbase have also heard a lot about poor service there and on GDAX. It's partly why I have never used them.