I think Doug covers it pretty well.
One way to ensure a UI works is for the implementers to have to use it "in anger". This is a tough call with CAD, I know, but PTC needs to integrate some real designers into the team who will tell it as it is in the pub after work.
Apparently little things in the workflow make so much difference to ease of use. There is no justification for all the menu manager, toolbar and dashboard variations. Consistency, e.g. you can select on screen or in the tree helps learning so much.
I would take a decent bet that Microsoft Vista people used XP for their work. They would never have stuck 100 dialogs a day asking if they "really wanted to run what they had just double clicked". The Win 7 people probably used Vista and fixed it rather well.
FWIW
John Prentice
ps - Thanks for the diremsion/symbol text size question and answers - Why should that be a hidden option?