It may be better covered in the techniques which we can change more easily as the support increases. I hate having to explain what a user agent is. Maybe we could make the guidelines match what is supported now and provide a link to a bulletin board for current information. The problem is resources to maintain it. We need a better solution.
Resources is one problem.
But at one point in time, we assumed there were only 2 browsers. Now the number of browsers is increasing. I support Kynn's suggestion that we cover these in the techniques. But some are so globally important that they need a place in the guidelines. We should state the requirement but the technology my eliminate the need for it.