I think the problem is that most "experienced" people aren't like the OP. People are taught from the very beginning that people will leave if they find out that you are new. Here is my story:

I was a MRD, and new to the game, as was most everyone else (this was right around release, so everyone was new except for legacy). I queued up for Sastasha, and waited, anxious about my very first dungeon. DF pops, I accept. I felt obligated to be honest with my group, and inform them that I was new, so I did. "This is my first dungeon. Could you please share any special tips that I should know. I read a guide online, but haven't actually run the dungeon yet." I said. Oh wait.. The healer left? And the one DPS? Wow..

The VERY first dungeon, less than a week after release, two people left my DF group because I was new. This is why I can understand people not wanting to be open about being new. That being said, I strongly disagree with flat out lying, especially when joining a pre-made /shout group. But ever since my very first DF experience, I have always been afraid to admit that I am new to a dungeon. I am still honest, because that's just the type of person I am, but I also usually have a healer friend queue with me. Worst case scenario with my own healer is that we have to wait two minutes for another DPS if one quits.

My advice to the people that want honesty in DF; Make it clear that you just want to help. If you just ask "Is anyone new?", then they will likely assume that you are going to quit if they are. I know I still assume people will ditch if they know someone is new.