The author of the newsgroup post, Ian Hickson, also works full time for Opera Software—the maker of the Opera Browser—so I'd imagine Opera shares a similiar path as Mozilla. Here's my favorite quote from the post:
> so I just don't buy that its so complex that that our weary little
> brains will melt.
Many authors I have spoken to disagree. The entire concept that your form controls aren't what gets submitted is very difficult for many people to understand. You have to realise that for many people, even the concept of CSS is hard to understand. People ask "how do I make this text blue", not "how do I make all my headers blue". The former is answered by the WYSIWYG mentality, stick in a <font>. The latter is answered by the semantic/style divide mentality, mark up the text as being a header, then add a rule to your stylesheet that maps headers to a colour.
In XForms the problem is even worse -- "how do I disable this control?" has the answer "you tell your data model that the relevant subtree is no longer relevant, then you bind your subtree to the control". People's brains dont melt -- they just go elsewhere.
I've felt that way since early on in the xforms spec. If you have a chance, read the entire posts, it makes a lot of points I agree with. I think XForms has a place, but a lot of things will need to be by the community first before every browser ought to natively support it.