32nd Legendary jimbo
To expand a bit on what phoenixfire was saying, the DF pedia does indeed use a different format than the other game encyclopedias. The Dragonpedia Masters group was set up so we could more closely monitor the 'pedia submissions and cut down on conversation, questions, and spam in the 'pedia entries. Any DF player who frequented the 'pedia before the changes will tell you that there used to be *a lot* of garbage posted regarding farming, drop rates, etc.
So. Rather than close the 'pedia to public posting, the Masters group was formed. It's a good compromise which cuts out all of the nonsense but still allows interested DF players to help out the 'pedia AK's and be included in compiling the 'pedia. The other game encyclopedias do things differently, so they don't need a separate group. But it's a necessary part of the DF system, which is why the group exists.
As phoenixfire said, any members who make an exceptional contribution in any area of the forums would likely be considered for Helpful/Constructive/Friendly/Creative title(s). They exist to show that the forum staff has recognized the contributions of the title holder - unlike the Masters group, which is just part of the inner workings of the DF 'pedia.
That said, as a forum group, I think the Dragonpedia Masters should be listed under the "Regular Users" section. After all, it's the only public group which isn't there (as far as I could tell, anyway). However, don't expect a separate group for any other encyclopedias unless the posting format is changed. MQ, AQ, and WF do things differently and don't require member groups.