Interesting, I saw it the other way at least there is no single supplier...The best way I found to think of it was (though your mileage may vary with the analogy):

DMD - gave latest features - its the shiny concept super car reference that shows whats coming next..

LDC - is the production sports car -integrates with rest of LLVM - and occasionally surprises with innovative features like Nicholas Wilson's brilliant D-compute.

GCC - its the production workhorse, fits all pipelines, goes where you need it and does it with style - its the muscle car of D world.

You pick the one that meets what you need/want.

Ian Buclaw has really done a superb job piloting this into GCC and hopefully GCC support might get you to look at D again :-).