I'm surprised this has not been mentioned: Accumulation of capital stock. (Perhaps this is what was meant by the first item?)
Wealthy countries purchase capital, tools to produce new products. While some of this capital (education, computers, welding tools) is mobile, much of it is not. This will remain in the wealthy country and continue producing products and keeping a high standard of living.
In economics, the hog's share of the difference between developed and undeveloped countries is capital, however, there are numerous ways in which a country's institutions can inhibit or enhance growth (democracy, corruption, etc.). Once a country reaches a "developed" stage and has reached a steady-state of capital, additional growth is achieved by technological improvement.