Ther is a new wish I thought to pose a comment on, but I can't find the option to do this. I have looked, and there are wishes I have commented on. Have comments been deliberately disabled? 

You may need to press the login link on the top right of the screen while the wish is open in the same way you need to if you want to vote on the wish.  This is regardless of the fact you are already logged in to view the wish in the first place.