It's not difficult to image the same sort of steel frame supporting a more recent skyscraper. However, Sullivan did not simply accept the structural engineer's geometry and simply mimic or represent it on the facade.
Instead, the steel columns are coordinated with the overall geometry of the building such that every other masonry pier contains a steel column (and is therefore structural). Therefore the alternate piers are non-structural.
Some might believe this to be an example contradicting Sullivan's famous dictum that "Form follows function." From Sullivan's viewpoint, I don't think he saw any conflict whatsoever.
I believe his understanding of a building's "function" to be much more than the technical realities hidden within the construction.
The so-called Functionalists have completely misunderstood and misinterpreted Sullivan's concept regarding the function of architecture. Rather than some form of materialism, truth to materials, or the representation of a building's internal functions, Sullivan conceived of the function of architecture to be among the highest expressions of a culture.
So a building is meant to satisfy deeper, more fundamental needs of a spiritual and psychological nature rather than an expression of mere matter.
I believe Sullivan's ideas of "Organic Architecture" have been similarly misunderstood and misinterpreted by generations of architects attempting to follow his principles.
HABS (Historic American Building Survey) project from a very similar viewpoint (compare to above construction photograph).
The construction photograph above was published in James F. O'Gorman. Three American Architects: Richardson, Sullivan, and Wright, 1865-1915. Chicago & London: The University of Chicago Press, 1991. The image appears on page 100 and is captioned as follows: "Figure 64. Adler and Sullivan, in construction (L'Architecture, 1894: University of Pennsylvania Library; photo courtesy of George E. Thomas)."
For additional information on the Wainwright Building see: Saint Louis Historic Preservation, Great Buildings Online, and The Library of Congress. You can search for many other photographs of the Wainwright Building on Flickr.