The lenses differ in the sensors they're built for.
EF-S lenses are built for APS-C sensor formats (canon rebel series, 60D, 7D), while EF lenses are for both APS-C and full-frame (6D, 5D's, 1D).
In 35mm equivalents, the EF-S 15-85mm acts as a 24-136mm lens, which is indeed a standard zoom lens, even if a bit long (24-70 can be considered the quintessential standard zoom range). In the same vein, to achieve the same range the EF 17-40mm offers but in APS-C format, you should find yourself something in the vicinity of a 10-25mm. Canon conveniently provides a EF-S 10-22mm lens, although without fixed aperture.