Combat swords as a build and gear set up have proven, time and time again, to be the highest sustained DPS available currently to the class. Daggers fall behind due to the spec (+5% crit != free swings), positioning issues, and energy-to-damage ratio.
There are plenty of swords available at 70 that are far, far better itemized than the Night Blade. The armor-ignore is nice, but not at the cost of more important stats (hit, agi, etc).
Durability doesn't work like that. The percentage is a fuel gauge to when you need to repair, not an active part of the combat mechanic (well, until an item is broken!).
Caring about armor ratings for a rogue is fail. Don't care about them, you should not be getting hit normally in an instance or raid. And for soloing, if the mobs aren't dead too quickly for this to be a non-issue, you have other problems.
Read the stickies here or google roguecraft 101 and learn the basic mechanics of the class if you want to improve. Don't just blindly do what "everyone says", understand why they say it.
Daggers in ShStep is fail. Why do people hold onto that belief?
Happy hunting