Just to add a few comments:
1. I'll apologize for the rudeness on the first page of this thread. I see nothing in your question that implies an inability to learn. Different areas have different practices. Where I learned in NC, almost everybody dove Nitrox for every dive. Here, in South Florida, the beach divers never spend the extra money, because we usually run out of air before we run out of bottom time on shallow dives. (After all, after 2 hours underwater, it's time to take a surface interval, don't you think?) Ignorance of this or that fine point in dive training doesn't imply stupidity. I, for one, have limited drysuit experience and have never dived with a rebreather. Am I ignorant of those types of diving? Abosolutely! Am I unable to learn? Not hardly! The tone set by those early responses really chaps me...
2. There are a number of reasons for the development of different terminology for enriched air diving. The use of enriched air is still a bit controversial, and some of the training agencies resisted its use until recently. Thus, the confusion over terminology.
3. Nitrox is used to extend bottom time (NDL). As a pleasant aside, many divers (myself included) experience positive subjective effects from the increased partial pressures of oxygen that you breathe on a nitrox dive. I seem less tired and feel a little better, but thay may be placebo effect.
4. Nitrox adds a safety concern, namely oxygen toxicity. Depths are limited to shallower depths than those allowed with air, for the oxygen in the gas can become toxic at depth. The bulk of training in Nitrox use (at least for PADI and IANTD, who certified me) involves calculating oxygen exposure limits to prevent the onset of toxicity, which can include seizures at depth, which are almost invariably fatal. MOD means Maximum Operating Depth. The Contingency Depth is a depth to which you can descend in an emergency.
5. The bottom line is that if you don't have Nitrox available locally, it's probably not worth taking the course. Sounds like there are other training courses that might be more applicable to the types of dives you do. Nothing wrong with the training, but if you're like me, you have to choose your training program based on things that will improve your skills and increase the safety of your dives.
Good luck with AOW. Keep gaining experience and training. Safely ascend from every dive.
-Grier
If it's not necessary then don't spend.
