Mesmer Armor bonuses

I know that you only need one piece of knights armor to get the absorption bonus, I was wondering if this works the same way for other classes, like if I have one piece of rogues armor, does my whole body get +10 vs physical?

No, you don't. The knight's armor is bugged - that is the only reason you get it all over. A.net is eventually going to fix it... although they have been kind of pokey with it. Armor bonuses should just apply to that single piece of armor - if they work any other way then that mean there is a bug.

+15 armor while casting (Noble/Performer/Virtuoso) is global, so having gloves of that set will give +15AL globally while casting.

Same bug as Knights on those. Maybe fixed later as well with the knights.