that's obvious and it goes both ways - i can only claim to have been involved in computers since 1984/85. Since then i've built a large number of 'white' boxes for myself and clients (with ongoing service support). I would have to agree with you re the modern boards and the power switch (btw there would be less confusion if we just called it the 'on/off/reset' button - still get asked by some of my clients "where's the reset button?").
re: you hold the "Power" button for those 5 or 6 seconds .... there are always exceptions to the rule. Like you can hold the on/off switch in for as long as you like and still nothing happens - except your finger turns blue.
re: I have seen at least one computer BIOS setting ..... every ATX motherboard that i have seen so far has that option plus more clearly visible. (i'm talking about retail motherboards, not OEM such as IBM, Dell etc. - you would, with your experience, appreciate the difference)
re: Like you are seeing smoke and or flames coming out of the computer ... firstly, you can say, with a high degree of certainty, that the computer has been "fried"; secondly, in this scenario, never ever advise anyone to pull the AC plug out the back of the computer - first action will be to place a hand on top of the computer ( smoke/flame = short in the power supply = unknown path of electricity = possible painfull electric shock and at 240 volts AC, in my case, that aint pleasant). I've actually had the experience of the plastic encasing the ac cord melting due to a short in the power supply (but that is another story). Anyway i now keep a small CO2 extinguisher handy on my work bench and in my office.
re: The switch is only a momentary-action switch - it does not have a defined position or other position, such as flip it up and it is on, and flip it down it is off .... ah, that's a typical definition of the reset button. And, in fact, all it does is temporarily bridge two contacts in the switch casing. When you release the button the switch itself returns to the previous state. The power button, however, in all of the cases i use has a definite on and off position even though you cannot see it by looking at the switch button.