(As posted at Guildwars2.com Forum)
Since Dual-Wield is exclusive to Thieves, on different weapons, only Skill #3 is dual-wield, but on same weapons, like P/P and D/D, all weapon skills should be dual-wield not just #3.
This way, D/D will be very different from D/x variant, same goes with P/P and P/x variant.
But that’s just me. No way Anet will do that anyway.