[DF] 40 Days Travel Time?

[JMason]

Ignoring the rules in Wilderness Adventures for the moment, DF2 offers up using a set amount of time for travel. The example given is 40 days and nights.

This has always struck me as very long. Does anyone actually run games that include this length of travel? I had my PCs go on a 20 day trip and it has been a logistical nightmare to get all the food they need. They ended up buying a wagon and 2 horses! And with random encounters, we only got 1/2 way there in our last session (and they are using quick march to shorten this to 10 days!)

I'm not planning on altering my game to make travel longer, I was just curious where this time came from. Is there some president in "old school" games?