The Glorious Quran says Middle nation, not middle city. That includes all Arabs and Arabia. In light of the Glorious Quran's numerical and geographical Miracle, I find the Hadith means exactly this: The sun prostrates to Allah Almighty under His Throne when it is above Arabia - facing Mecca.
And like I mentioend in the article, how this works while it is in motion remains in the unseen world, exactly as Allah Almighty said.
As to Mecca's meaning, I don't think it means center. But when I get a chance I'll try to check it out, insha'Allah.