Originally posted by Count Six
I intended it for game-balance. Bosworth raises tax value +1, regardless of the path after Towton. With the "Yorkist" path, the player/ai gets faster revenue growth (and some infrastructure also) because he gets the temporary "Clarence" revenue increase as well as the permanent "Bosworth" increase, but at the cost of repeated stab hits and revolt risk. With the "Lancaster" option, the player/ai gets lower income, since Bosworth merely compensates the loss from Henry VI's misgovernment; but on the other hand, there are no stab/revolt penalties. So in other words, the Yorkist option is high-risk/high-yield, the Lancaster option is safe but low-yield.
My theory is that a "Lancastrian" succession into the 16th c. rules out the administrative and fiscal innovation of the Yorkist and Tudor dynasties - the late-medieval status quo prevails, with a weaker, poorer monarchy. No pain, no gain. On the other hand, what used to be called the Tudor "New Monarchy" comes at the price of labor pains - in the form of the WotR instability.
I've added an event called "The Lancastrian Succession" in July 1483, which explains this alternate history and, to ameliorate the Lancastrian "revenue penalty" slightly, adds +1 stability.