Dear Lazy Tumblr
By default disqus wants you to throw in their code at the end, before the {/block:Posts} so every single post type gets the default treatment of the disqus comments and comment box. But if you wanted to enable it for certain types of posts you would throw in the code that disqus gives you not before the {/block:Posts} but before the blocks you wanted to enable commenting for.
But there’s two bits of code disqus wants you to include. The first bit does the comments (x) part, and the second bit does the actual comment form.
The comments (x) part can go, as you said, inside the the {regular} block, instead of after all the post type blocks. But the part that makes the actual comment form has to go inside the {permalink} block, which renders on ever post-type’s permalink page. If the comment form code goes inside the {regular} block, then it’ll render a comment form on the main page as well as the permalink page.
It seems that what I’m asking for requires some CSS-fu of the sort that Paul Giacherio’s siloTheme uses, or Nostrich uses on Peacock Tail, to get different styling on the main page and the permalink page, but then goes further and has different styling on the permalink page, depending on the post type.
Hmm… I know I left my too hard basket around here somewhere.