Adrian,
Finding myself with far too much spare time on my hands last weekend I decided to put some serious thought into your question and came up with the following :
1. 15th/16th Century Landsknecht formations contained a Rottmeister.
2. Could not think of any other valid reason for it's demise over a fairly short time frame in the 17th Century. (must have been an epidemic outbreak)
3. The disapearence of the musket rest over the same period ( cross investation ? )
4. Nobody in their right minds would have come up with the concept of the plug bayonet unless after repeatedly shortening your pike to cut out the rot all you where left with was the head plus a few inches of the wooden shaft.
Taken collectively I think the above points answer your question and I now feel justified in downgrading Peters Parliamentarian Pike before our next game.
I may now post this on TMP, I'm pretty sure someone on there will agree !