As one of the organisers of the Dukeries Ultra I thought I'd add a comment here.
We included the provision for a drop bag for a few reasons:
1: We wanted this to be a fast route, and so the drop bag at half way means that you probably don't have to carry as much kit/food with you.
2: We wanted to give first time ultra runners a flavour of the longer events where you do get drop bags
3: A chance for anyone doing longer events later in the year a chance to practice with a drop bag and see if they pack what they actually need or what they think they need (also good for number 2 above) A bit tenuous I know as how you feel at 20 miles is going to be a little different to how you feel at 50!!
4: To give ourselves an extra logistical headache, because organising a race through 40 miles of forest and country park for more than 100 runners is just to easy otherwise 

RLS
Edited: 17/05/2012 at 09:50