A few points
1. THE Rulebook, the rules have been rewritten or were reviewed about 6 times by the original designer as well as hobby people over the course of its 50 years. The rules are geared toward Face to Face play. The idea of no discussion during adjustments and retreats is MOSTLY to speed up the game and also the view that in the case of the retreats the action is taken more as a matter of on the spot choices.
2. The rules were written to cover BOTH the case where the player leaves the table and where a player totally screws up his order.
3. In face to face, world class tournaments, there have been numerous variations on the Removal Rule in CD, and a few attempts at the retreat rule just to cover player screw ups in orders, as well as the CD situation.
We almost had a complete revision of the removal rules in the 1999 board game rulebook but an unfortunate internal issue in editing by Hasbro messed it up. The new rules were a direct copy and a NON-reviewed version at that.
4. In the net world, there are places that use a different approach to the removal of units that have not been ordered. One such place is www.Stabbeurfou.org and I think the other is 18Centres.com(but I do not recall exactly what this one does). These variations tend to be in the House Rules
For those that care, this is my approach
1. In FtF games: no discussion 20 seconds and time runs out.
No build if not written, retreats: off the board, for removals the sequence is:
a. Non owned space
b. Non owned space not adjacent to an owned center
c. fleets before armies
d. then alphabetical
2. For email: short deadline between moves, negotiations allowed and in deed encouraged. If no orders in a build I prefer an AI build or a sequence such as For England and Italy: Fleet then army then fleet starting at London and Naples, for all others Army-Army-Fleet starting at capital.
Removals as above.
It should also be pointed out that I am in a very small minority on the views on builds and most overwhelmingly prefer miss order=no builds, though most prefer the removal sequence of adjustments as I outlined above.