My $.02 for what it's worth..
First, if someone explicitly described the difference between multi-gas diving and single gas diving (tri-mix etc vs nitrox) I apologize...I think it is worth emphasizing the difference on this thread vis a vie requiring dives...there are specific in water skills you must learn and be proficent at to safely dive multiple gases...you will typically be diving with at least triple the number of tanks, usually...that is, doubles on your back and a slung tank-that affects buoyancy, and equipment stress levels. In addition, there are conventions in tank marking you must learn and you must demonstrate your ability to recognize those different gases and then switch to them underwater...that can only be suffiently tested under dive conditions...
Nitrox (EAN) on the other hand is typically a one gas dive, unless it is one of the gases used in the multi gas dive....I am afraid I am not being clear, but what I mean is I REPLACE air with it on dives, but do the same KIND of dive, as opposed to a mix dive, which is very different.
Therefore the in water skills for EAN are no different, so dives are not required.
Two excellent points above deal with the idea that the "dive" begins when you arrive at the boat and ends when you disembark...to that end, dives along with the course are useful, but not necessary...
I did TDI, and we had no dives. Our training, in addition to the math, was from "arrival" at the shop to "embarking" on the boat-planning dives, analyzing tanks etc.
We ran scenarios in class that addressed changing the dive plan on the fly...
As a by the way, I use a computer as a unnecessary backup to my brain-I am not only ready to change the dive plan on the boat, but under water if necessary...
So bottom line here...
1) tri-mix and EAN are too different to compare
2) Dives are not necessary for EAN, but more dives under supervision are NEVER a bad thing!
3) "The dive" is more than the wet part, and whether you "dive" dry in your EAN course, or wet, it is still important to think that way...
Finally, may I beg all of you to try to keep these discussions focused on questions and answers...how does any negative statements about someone else promote knowledge?
Just my thoughts...I would welcome others insights...
regards,
Ken