A check of the official geographic names index (GNIS) of the USGS reveals that the name of the high point in Arkansas is "Magazine Mountain", not "Mount Magazine". Although not a hard and fast rule, generally "Mount Xxxxx" is used for a peak, and "Xxxx Mountain" is more frequently used for ridges, which better describes this feature. Magazine Mountian appears in the GNIS as a ridge, and Signal Hill as its summit. "Mount Magazine" is the name used by the Arkansas State Park, but it not the officially accepted name. All four of the guidebooks published to date on state highpoints have used the correct nomenclature, and I believe entries in Summitpost.org should do the same.
Pretty much most references in the local area (of Arkansas) call this area Mount Magazine. Signal Hill is the official summit. I don't see any reason to change based on the USGS official names, when the whole area is called Mount Magazine State Park.
I believe you are correct, sir. There is a lengthy discussion of this on the additions/corrections section on the main Gannett Peak page. Probably should read "most glaciated outside of Washington" or something to that effect. However, as I didn't write that particular section of the page, I will let the author weigh in with his opinion.
The original source of information about this, I believe, was the Winds guide book. I'll take the USGS source of information as a better more reliable source of information with data figures, so I will change this statement in the article.