When you right-click your table_data and select "Add to Watch" and run your macro again, is the "Value" showing up as "Nothing" in the Watch Window?
This isn't related to your issue, but it appears the Wiki changed formats since this tutorial was posted. Once we get this issue resolved for you and you get to the final scrape_wikipedia_pop_data macro at the bottom, you'll eventually need to change
Set mtbl = webpage.getElementsByTagName("Table")(1)
Set mtbl = webpage.getElementsByTagName("Table")(0)