I think tiles tend to attract a wider user base, who eventually move on to the ASCII version. The Crawl poll showed that a lot of people who play crawl either play the tile version currently or started with the tile version. With Dreamhack and Grendel's Mother, I've only ever had about 1 download per day, where as the tile based Crawl gets many, many more than that. Of course, this isn't a fair comparison since Crawl has been around for so long and is so popular.
Still, I think that tiles and better graphics in general attract new players. I've read a lot of stories related to the crawl poll that go something like "I use the tiled version to show my family and friends." Since most of our distribution is likely word of mouth, graphics may particularly help us reach new audiences. The entire computer industry moved toward better graphics in part because it was attracting so many new users.
That's not to say there is no room for ascii! The crawl poll also showed that a lot of the people who started with the tiled version moved to the ascii version. I just think that a tile based or graphically pretty mode is nothing to be ashamed of in roguelikes these days. Better graphics can lure new people in, and I think that's something to be supported. Especially since there are no more commercial tile based games anymore, anyway.
Better graphics are like better advertising, they lure in more people. I'd personally love to see what developers came up with as graphics for their roguelikes..