With the otaku in full hue and cry over the editing of manga for American release (see 'Viz Responds to FMA Edit'), now there's an analogous situation with that most American of American publishers -- Marvel.  The Groovy Age of Horror blog has published comparison scans of Tomb of Dracula #5 (the b/w magazine from the late seventies and early 80s, #5 was published in 1980) and Essential Tomb of Dracula Vol. 4, released last year.  Numerous edits were made for the Essential volume, covering exposed breasts.   

At the time this Tomb of Dracula issue was published, the Marvel b/w magazines (Savage Sword of Conan was the best seller) were sold on the newsstand and in comic stores with the understanding that the newsstand size, trade dress, and presumably racking (because of the size) made it clear that they were not comics for children, but were instead something for older readers, although they weren't labeled adults only. 

The Marvels were tamer than the contemporaneous Warren magazines (Creepy, Eerie, Vampirella) by far.  The Warrens, in turn, were probably less explicit than the cutting-edge Heavy Metal, also magazine size and distributed on the newsstands, but in color.  And all of them were reacting to the underground comics, which began to flourish in the late 60s and continued unabated through the 70s, where literally nothing was out of bounds.   

Marvel continues to publish material only appropriate for adult readers, using labeling to identify the audience for the contents.  In this case, Marvel may have chosen to edit the pages because the previous volumes of the Essential Tomb of Dracula reprinted material from the Tomb of Dracula color comic, which was code-approved.