Yes technically you're right there is a 375' height limit, but as DC Res pointed out. That height limit isn't going to stop a developer from building, IF The market demands something taller, as has been the case with 111, The Reget, 151, The Regent Hotel, 222 etc etc.
There are a few plain and simply facts as to why Salt Lake City doesn't have more skyscrapers. Availability of land, there is still so much available, and in large chunks, the second is just as important if not more so, DEMAND. When there is a demand for taller buildings, we will get taller buildings. We got a taller than 100' mid-block residential tower why? Because there was a demand for it. We got 222 and 111 office towers, one taller than the mid-block 100' and one taller than the corner 375', why? DEMAND!!!!!!!!!
Until demand increases and land availability reduces we are going to continue to see buildings in the same basic height range.
I know several differ on this opinion, but I'd rather have a more evenly populated downtown with multiple 350-450' buildings, such as 111, 222, 151, than one 600' building.
I'm not sure that the cialas/viagra comment was made in the appropriate direction. Whoever set the 375' height limit obviously didn't feel the need to over compensate, which apparently several demanding a 600' building rather than a more balanced downtown must be doing just that.
As for LaSalle, if they end up building a residential unit adjacent to the Utah Theater they are going to build something that either compliments Main St, and is a height within the historic fabric of the area, or they are going to build something of a decent height, maybe not skyline altering but not a 4 story on a podium design either, why? Same answer as above, DEMAND.