I have only ever seen one car advertised without the ML, and I was quite surprised because I thought it was a standard fitment\default option.
With regards the TVD I would agree that it probably doesn't have a great impact during day to day driving (assuming you're not pushing it everywhere you go) but the cost of this as an option vs. the £18k plus for the diff as a spare part seems it will make cars with a TVD more sought after in the future.
When i was looking for mine I had the choice of a base car with only ML, about 10k less mileage and in very good condition, or a car with all options (including the light grey leather which i like as lifts the interior) and about 10k more miles and not such perfect condition. I went for the fully optioned car as I like my toys, don't do a massive annual mileage and i hope will be more desirable come resale time.