I actually did a couple runs of PotP last night with a full group. We started in on hard then elite with 10-12 level characters then did 3 elite runs with our 14s. Nothing good to speak of really but it was still fun because of the group.
Hit the Necropolis pretty hard the week it openned up but Ill generally hit any quest on the LFMs thats in my level range. Way more fun than rerun after rerun imo. Honestly I think we just plain need more ppl playing, but as time goes on I think it will level back out between GH and the Necropolis.
To the OP welcome to MMOs'. Its been this way in every game I could think of. Even seen the other games encourage this by adding bonuses to XP or loot tables for running the new content, or desired content of the month. Not needed here, people automatically move to where the new content is because there is new stuff. Old stuff they have already. New stuff is often better than old stuff. New players to the game will probabley end up skipping alot of content to catch up with old players, and then there will be a phase of nestalgia about content. Like "remember when velah would throw you out of the instance?".
If DDO don't move up and move on then it will die..
Yah khyber has definitely seen an increase in low level stuff. Late last night (11pm pst and later) there were multiple harbors.
It's a trend in all MMO's. Everybody wants to play with the new stuff. It actually gets worse as a game grows in age and there are more and more things added, the older areas get abandoned.