That is indeed a very useful information. When a skill tree is at level 100 the character can use that weapon/shield with any other vocation, right? Do the skills belonging to the skill tree be available, too?
For example if a character has the sword tree with a minstrel at 100, will he be able to use, let's say, Dragon Slash while being a priest?
Edit: Actually that is a pretty dumb question. If that was true then you would have only one "class" in the end...which would be stupid.