I apologize if I ask the following  obvious questions and perhaps risk wasting everyone's time.  But, I have these nagging questions for a while now:

1).  As I understand it, the 10 minutes delay is to create a new block that there's enough/ sufficient time to fill and confirm the transactions (globally).  But isn't it quite wasteful to keep adjusting the difficulty level to maintain the 10 minutes delay ?  What is so special about the 10 minutes delay?  Has there been any study to quantify more accurately the amount of time to reach the nodes globally ?