You're certainly right about the trend away from Royal Dukedoms. However because Prince William is a Heir Apparent (behind his father), he will probably get one on his marriage, and WILL get one once his Dad becomes King (he inherits the Duchy of Cornwall), while other members, including Prince Harry might not a dukedom (especially after it's clear he will probably not ascend to the throne because Prince William have children) because they're not as close to the Throne.
Again you're right that they want to lead a more normal life, but being a Duke isn't going to get in the way of doing that though. One of the main reason he may get a Dukedom is so Catherine won't have to be called Princess William (officially anyway), but can be called by Duchess of X (or Countess of X or the feminine form of whatever title Prince William get).
I should point out though that Prince Edward is really not in the line to get Dukedom of Edinburgh, as it can only go to Prince Charles. There's a thread about that on the top level of British Royalty forum.
And before I forget, welcome!
Thank you for your welcome, Royal Eagle.
I fully agree that Prince Edward is NOT automatically in line to get the Dukedom of Edinburgh - it will revert to the Crown on the death of the DoE. I will go and look at the other thread. I did research this topic quite thoroughly - I have to have a working knowledge of Royal Titles in my profession.
Thanks again for the kind welcome
Alex