This is actually a question we've been asked more than once, so it's relatively easy one to answer.
The Flamingo wasn't one of the properties we randomly selected the last time we conducted this survey, so we placed a call to housekeeping this time and were told that, "The windows on street level get cleaned, but as to the guest rooms? We clean the inside, but the outside? It's been awhile." So, that could explain your lack of view.
Here are the results of our survey the last time we called around to answer this question (last year) -- and again, we'll note, those properties we called were surprisingly helpful, with one strange exception.
Skytag's the company that puts those huge advertising wraps on the façades of buildings and was in fact the subject of a recent QoD (11/13/2009). Once the sticky "spectaculars," as they dub them, come down, a cleaning process is necessary to remove any adhesive residue and they were more than happy to reveal all. Apparently, it's basically accomplished using a giant mop that comes out from the vents at the top of the pyramid. They spray water down the side and the mop, which operates on a cable system, washes up and down until the whole side's been cleaned.
While we're on the subject of windows, here's one last interesting tidbit. If you visit vegastodayandtomorrow.com, which we do with some regularity, since it's a very interesting site, you'll find information about the "window trick." When you're building a hotel with thousands of rooms, if you give each of those rooms its own separate window, the building's façades start to look very cluttered and congested, like a battery chicken factory. So, some smart architect came up with the idea of sharing one window between four rooms, which gives an altogether more spacious impression. Check out the link to see what we mean.