Well by no stretch of the imagination can you call them vague. Generally I would say that you should folow the guidelines, because they are what the browser authors will be reading, so having a common basis for design is a good thing. If your page validates well then chances are it will display in most browsers.
Generally speaking too, the guidelines are there for your own good. e.g. they say to use css for presentation. that actually makes your job easier, so IMO the guidelines are a good thing to follow. If you choose not to then that's your affair.