NAV Canada runs the air navigation systems at major Canadian airports. Apparently the height originally proposed would interfere with their equipment somehow, so they had to shave a few meters off the proposed height. Not sure if roughly 900' is the de facto limit to towers in Calgary or if its position at the east edge of the core makes it a bigger issue. The downside of the fact that, out of Canada's biggest cities, our airport is the closest to downtown.
The more I look at the new renders, the more I like them. I much prefer the more subtle roof pitch and the two buildings appear to be more distinct from one another rather than typical twin towers.