I bought a lot of roleplaying game books over the years that I never intended to play and never used any of the game mechanics. In each case I bought those books because I liked the art and the ideas the art inspired in me for characters or monsters. Not once was I swayed in favor of buying a roleplaying game because it included free nudity.
|Nymph, MM v.3.5, pg 198|
Dungeons & Dragons: 3rd Edition was an inspired reboot of a classic game but it wasn't perfect. The cheesy blonde nymph on page 143 of the Monster Manual (Core Rulebook III) wasn't much of a fey nor "nature's embodiment of physical beauty".
The v.3.5 update of the Monster Manual clearly tried to make up for the failure of the previous attempt. Elmore's blonde bimbo was replaced by a naked, but more fey appearing, porn star complete with areolae, tracts of land, and more.
As a father of four children, all of whom should play D&D like my wife and myself, I can say that I don't want this kind of art in my roleplaying games.
Kids play Dungeons & Dragons. I started playing when I was ten years old (yes, I know that was a long time ago). D&D is an all ages game and the art in the only mainstream tabletop roleplaying game does not need to provide titillation.
As a business, I don't think the nymph in v.3.5 of the Monster Manual sold extra copies of the game but I can feel very confident that there are parents who will skip buying books that cross the line. While I have not made an exhaustive analysis of 4th edition art, in this regard I believe that 4th edition has actually gotten slightly better than v.3.5.
The art in my Dungeons & Dragons books is important to me and important to why I enjoy the game. If done inappropriately that art can get in the way of fun and ultimately send me elsewhere to spend my money.