Fair enough. Large memory is needed for some developers and the 16GB option should be there. But for many, many developers, a few GB should be more than enough.
I'm in the same boat and actively looking at the XPS-13 (have one in cart as of writing). Dell Tech support suggested this limit was due to the motherboard. I would imagine another refresh will be coming -- either with Windows 10 (Sep/Oct) or Skylake (Aug).