I can only spec that if browsers are willing to do it. So far, my understanding is that they are not. (There’s no point writing a spec that isn’t followed, the whole point of the spec is to define what should happen to get interoperability.)
Whether the vendors are right or not (perhaps it is really a nonsense idea), if you make this quote less specific it equals:
Making specs for HTML5 is useless in this WG, vendors will do what they want, not what we specify they should do.
Pretty ugly isn’t is. Why is there a WG (with vendors like Microsoft, Mozilla, Opera etc) as the vendors decides what is best for us (from their perspective) instead of what is best for us from an independent (WG) perspective. This mindset is not what you need for a proper specification. A proper specification should be made without any restrictions or wishes a developer has and should be fully focused on what the customer (you! the user of your browser) wants. The customer is represented by the WG, the developer by the vendor.
Conversations vs demands
Off course you will get a better result when specifier and developer will have dialogue about the specs. Both have specific insights and specific knowledge. Combining these two will increase the quality of the specifications and more important: will increase the quality of the product that should be build. The current situation with HTML5 is that some developers won’t develop certain functionalities. Since this is known by specifiers this is accepted and specs are adjusted to what the developer wants to make.
Why is there a working group? Vendors decide what they will implement and what they will not, the WG has not any influence on that decision and is currently even writing specs that taken this stubbornness in account. The HTML5 WG is therefore useless and is only useful to write down what the developer wants, not what is good for the web or its future. Why should the WG even bother to discuss certain items, ask what the vendor wants to implement and make this the specification. It is a good thing that vendors participate in discussion, however when it comes to implementing they should follow the specification and recommendations. They can give advice why things should or should not be implemented from a technical perspective, however they should not ignore specifications beforehand.
Both WG as vendors are walking on thin ice as we speak, the WG is specifying what the vendors want and not necessarily what is best for the future. The vendor does not want to implement functionalities that seems to be preferred by the WG and is not showing any vision on what is best for the of the web (assuming the original ideas of the WG are best).
Both parties are responsible for creating a product (HTML5) that could had been rather revolutionary and could have been a major improvement for the web, instead they will create just an upgrade of HTML4 with minor impact. Just because vendors are to stubborn to listen and the WG is too passive to make the specs that matter and instead it is making specs a vendor prefers to have.
Vendors should take sponsorship as soon as a WG starts. With this sponsorship they commit themselves to the outcome of the WG discussions (of which they could be part of). That is a whole other ballgame, however I think it can increase the innovation for the web.