[Marileangorifurnimaluim]

I tend to think technological advancement comes from individuals as well as a supportive society (read peaceful and wealthy) rather than simply being a factor of time. Add to that the influx of fresh ideas from differing cultures, as well as the freedom and resources to develop them.

Research shows that the British Empire edged out France as a world power because they produced staples, essentials, while France undermined their own economy by focusing on luxury items (very profitable for individuals, but not a stable base for the country as a whole).

Technological advancement in the US was based on the exploitation of massive untapped natural resources. One example: the entire state of Michigan was covered in old growth hardwoods the size of what we only find in the National Redwood forest today. It was denuded in only 100 years. Staples for the world. Not to mention our gold rushes. This is the basis for our technological advancement. Wealth. Outside of the revolution and the civil war, although the US has fought many wars, virtually none of them were on our own soil. Peace.

Most of the advancements you list, Mho, come from another wealthy and peaceful country, China. Stirrups, came to us from the Mongols. Paper and Gunpowder from China.

So, using our own world as an example as you do here, and three requirements:
1) indepedence and will to change (advancements were not made by the west until the shackles of the feudal system was removed)
2) wealth to do so
3) peaceful circumstances, time to do so

.. in Middle Earth, where would the technological advancements come from?

Gondolin had peace and wealth for a time, but little contact with the outside world. So their advancements would never have gone beyond their realm, and there would have been little impetus to change.

Moria, the dwarves, ah, they did have technological advancments, the delving and tempering of mithril. Their society was hampered by an inconvenient balrog or so. Goodbye peace.

The race of men were vassels to either Morgoth, Felagund, or the Valar, and later Sauron. Numenor and the elves were vassals to the Valar. Sorry. Even well-intentioned, it caused both the elves and the Numenoreans to look to the Valar as the source of knowledge. Feanor and Celebrimbor were exceptional in a culture that looked to the Valar for answers.

And while the wealth and power of Numenor increased, again we have the problem of will. They yearned for Valinor. Their technology did advance, especially their navy, but they were like the society of ancient Egypt, obsessed with death.

Actually, I can't say that the lack of technological advancement is a bad thing necessarily.

Certainly not when I look about the open spaces of Michigan and picture the forest it once was.

But then, that is an Entish sentiment, isn't it?