I think this is the right of it - it is easier to cast spells in 3E because the chance of disruption is/was minimized.
Exactly. I think the change MM is talking about is that 3E has "encapsulated" actions - you're frozen in time until the start of your turn, then you take a turn's worth of actions in a world of statues, then you go back to being a statue yourself and the next guy animates. Certain actions you take can animate the guy next to you long enough for him to make an opportunity attack, but you have control over that and can plan for it.
Pre-3E, initiative worked rather differently. As I recall, everybody declared what they were going to do, rolled initiative (every round!), then did it in initiative order. A caster who rolled poorly on initiative could be attacked by a monster with a better initiative roll, and if the monster rushed over and whacked the caster, the spell would fizzle without so much as a Concentration check.
I certainly would never advocate a return to the old system. The new one is far smoother and less cumbersome. But it did have a drastic effect on the balance between people whose actions could be disrupted and people whose actions couldn't be.
This seems a very one-sided view of 3E casters. Those of very high level - sure. But what about all the weak-arsed wizards that died before they got anywhere near this high-a-level? What about all the wizards that needed the other classes to help them do their thing while they were nowhere near throwing out save-or-die spells?
If they were playing it smart, they more than pulled their own weight. Save-or-die spells exist even at level 1. See
sleep and
color spray.
A recent thread on fantasy fiction, computer games and D&D provided an interesting landscape of what influenced player's expectations and I think perhaps illuminates the thinking that goes into casters and their place in the game. For those of us who got into D&D through fantasy fiction, of course wizards were powerful - and when they reached this power, who could stand against them? The pay off to play this style is obviously that they started weak and developed in power whereas other classes had a more linear development. However, for those who have gotten into D&D through computer games moreso than fantasy fiction, the lack of "balance" is obvious (be it being weaker at lower levels or more powerful at higher levels).
I came in via fantasy fiction, but I take the "balance" side and always have. Level is an arbitrary designation. There's no reason why the uber-powerful wizard of fantasy fiction has to be the same level as the fighters trying to stop him, and without that restriction, the whole comparison breaks down.
IMO, level should be a measure of character power. A character who is uber-powerful, for any reason, should be higher level. If you want a world with uber-powerful wizards but no comparably powerful fighters, then put a cap on the level the fighter can attain.