Now devs who know more than me, correct me if I'm wrong, but I don't think any of these changes are mandatory. If you want, you could run an old version of litecoin-qt (or whatever), or even run your own wallet client thing. The TX fees are not required by the protocol persay, all that was being done was changing the default to accept them in a block and relay them...if I understand it correctly, you could mine blocks and not enforce ANY transaction fees, and no one could stop you.
The transaction fees are decided by the miners -- the miners could have rejected coblee's changes by not using the new version, and he couldn't have done anything. He produced a fix which most people think will work, so they switched over.
Exactly the old clients still work and if anyone wishes to use them to receive then propagate the spam transactions then feel free to do so, just don't come bothering us with the problems it can cause if you can't be bothered to upgrade...
The problem has already been caused - it seems that the attack was smarter than anyone realised (or more likely was smarter by mistake)
Many people now have 1000's (I have 6832) of tiny transactions that they cannot spend and need to be avoided or ignored for eternity.
They also exist in the block chain and will never disappear.