Intriguing, let me give it a shot...
I think your third point answers your first point.
The cultures that crossed water or land bridges were not ones that would have been able to, much less desire to use, draught animals. Sure it might be nice to have something to carry your belongings, but it was better to be able to carry it youself, or within a canoe (boat). And they were basically hunter-gatherers which meant they did not need to domesticate animals for ploughing as there was no ploughing to be had.
Without draught animals, or the need to carry massive amounts of supplies over land, the wheel was essentially useless. They may have understood circles or that hoops might role, but an axle and wheel would not be much use (except perhaps as a wheel barrow).
The largeness and diversity of the landscapes may have also ruled out wheels. They would not help on water, up and down wild mountains, through forests, etc etc.
I can't guess why the bellows were not developed, other than wood and stone were enough for most people's needs. They also moved a bit, often in smaller numbers than a normal ancient "urban" environment and so no one really had time to commit to looking at materials engineering.
That said, I thought some native americans had bellows of some sorts to stoke fires, even if not for smelting operations.
Does this make sense? Pure speculation of course.
holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)
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