I am more enthusiastic about this than Duncan: It's not just that a slots parlor will not be located on someday-prime riverfront property. It's not just that it won't add to traffic on a major north-south artery, and instead will sit on top of the nexus of subway and regional rail lines.
There are at least two other major advantages. It brings investment dollars to a part of town that has been allowed to become neglected in terms of amenities. The prospective audience for a slots parlor are suburbanites who might otherwise be afraid of coming down to the 9th & Market area at night. The casino company will naturally want the area to be neat, clean and lined with attractive, convenient businesses (besides the massage joints and pawn shops - we got those covered) that stay open late. But they will also be forced to integrate elements of urban life into their plan in a way that putting a huge self-contained structure out on the river would allow them to avoid. In other words, the casino will end up being more Philly than Generic Gaming Establishment, USA. Also, the added development may help to bridge the physical gap between City Hall and Independence Mall that tourists often find difficult to navigate. Currently, the Market Street space between the Mall at 6th Street and, say, the Hard Rock at 12th, consists of huge surface parking lots and office buildings that shut down at night. During the day is a long hike over a concrete plain to get to the fun and historic part. At night it's relatively safe, but it often doesn't feel that way. Adding a landmark, even if it's not the ideal variety, might improve a boring or vaguely threatening half-mile section of street.