Required vs. strongly recommended is an important distinction. Satoshi Dice reuses EC Keys for every single transaction. Exchanges will have the same address you deposit in over and over, which gets reused. This is a best practice argument rather than a protocol requirement.

On Sat, Nov 2, 2013 at 8:27 PM, Luke-Jr <luke@dashjr.org> wrote:

On Sunday, November 03, 2013 1:19:51 AM Allen Piscitello wrote:
> I actually had a use case in my case where it was possible, and that was
> the check I used to get around it, just configured it so that I always
> generated a new key when I needed to set up a 2 of 2 Multisig Refund Tx.
> It was either that or making sure I had no unspent outputs. The use case
> of doing it was laziness in just creating a single key.

Use cases mean an actual use, not mere laziness. Bitcoin as a system has
always required a unique EC key (and address) for each transaction.

Luke