Take the server technicians example for starters: Does online training really demand a virtual 3D environment? What would one learn in such an environment that could not be taught more appropriately with a text, video, and flat interactive media like Shockwave Flash?
Realize this: you are viewing the model through a small window, with no feedback and limited physics modeling. The virtual screwdriver doesn't have any weight, and it won't realistically fry the PCB (printed circuit board) with static if you accidentally touch the wrong contact.
Such hands-on experience would be best learned in a real environment, surely? At least until something akin to the Star Trek holodeck comes along. I am assuming here that by technicians Jeff means hardware engineers. The thought of having system administrators sitting in front of a computer which is running a 3D simulation of a sys-admin sitting in front of a computer is just too strange to even consider.
3D lettuce, anyone?
The online store looks more promising. But again, just stop and think about it. When doing your grocery shopping online, do you really want to pick up and examine a 3D lettuce? You've seen one, you've seen them all. And besides, it won't be the virtual variety that will be delivered to your front door.
How many products really benefit from close examination before buying? Books? Not really--a scan of the front and back covers would be enough. Flipping through a 3D book via remote control would be a bit of a nightmare. A flat Web page would be far less cumbersome.
Some products would benefit from a 3D model. Things that are sold on their looks as much as their functionality are the prime candidates here--cars, furniture, and so on. A virtual tour of a house on the market is another fine example.
But such purchases make up only a very small percentage of total products sold. Most things that we buy from day to day, we do so without the need for a tour of inspection.
The bottom line is this: New technologies like 3D should be welcomed. But just because they are visually impressive, does not mean that they have widespread applications. 3D does have some applications. But the vast, vast majority of Web sites out there, whether they be e-commerce, e-training or e-whatever, have no genuine need to model environments or products in 3D.
For the majority, 3D is just eye candy. And eye candy, as has been proven so many times in the past, tends to only stay in the spotlight for as long as it takes the next "kewl" thing to appear.
"Why hasn't 3D obtained online ubiquity?" For the same reason we've survived this long without really noticing it was missing.