I'm more of a Big Picture guy but let's try to look at some nuts and bolts to see how they fit.
Using Ken's
recent excellent update on residential construction we find that within the 1.5 mile radius of the D&F Tower over 6,200 apartments have been built since January of 2010. There are currently an additional 4,500 units under construction. There's also a good number of apartments being built outside of the 1.5 mile radius. I'll guess another 1,500 units maybe more. The total of over 6,000 apartment units under construction is close to the number of units that have been completed since Jan. of 2010. There's easily another 4,000 units in the pipeline.
Nobody could have predicted the strength in popularity of bodies wanting to live downtown. Development as we all know happens over many years. Within the next 18 months it's highly probable that we reach market balance and likely an oversupply of apartments.
Developers will continue to build up to a vacancy rate of 7% or more. For example Dallas metro has recently had vacancy of 7% or more but the growth and absorption is still strong.
With all of Denver's development (for the most part) being downtown where it's more costly to build, construction has occurred more methodically as opposed to the ease of building 3-story walk-ups in a Dallas suburb.
As to the Denver economy and continued robust growth downtown, that's for another, more speculative post. Things can and do change though.