First of all, I'm pretty confident that the new apartments being constructed by Cowboy Partners west of The Gateway are not income controlled.
Here is a link to a document that clearly states that it is market rate apartments:
http://www.slcrda.com/meetingsmin/2012/BOD/071712/8A_LibertyGatewayReimb.pdf If you're curious as to why projects like that are built, it's usually based on the type of financing the company uses for the project and frankly, because there is a huge need for it.
Now that's clear, I completely agree with Comrade that mixed income housing is not only a smart thing to do but personally I think it's the moral thing to do. (If anybody wants to hear my speech about why I think it's the moral thing to do, I will gladly share it with you privately)
It is interesting to see that downtown living seems to be a complete dichotomy with some of the wealthiest in the city juxtaposed with some of the least wealthy. There are not a lot of places that currently appeal to middle-class families at the moment but I think that's true of most cities. There is a draw for people to come back to the city but I think it's mostly made up of younger people/couples/families or retired people/couples. You are not going to see a huge influx of middle class famillies wanting to raise their child in a multi-family residential development until there are shifts in societal thinking. I'm definitely not saying that it won't happen but I think it's a ways off.
Lastly, if you think Cowboy Partners projects are "ghetto" then you need to get out of SLC every once in a while. I don't love all of their projects or proclaim them to be architectural gems but they are certainly not "ghetto".