Although this function appears not to be used in your example, is this a hint that if the widget is a container widget, the container's children have to be removed before the container widget is removed?
Have just finished writing the complete article.
I actually came out with two sample codes - Part 1 and Part 2 - each using a slightly different techniques.
Sample Code 524: How to unattach a widget from GtkTable or replace a GtkTable cell with another widget - Part 1?
Sample Code 525: How to unattach a widget from GtkTable or replace a GtkTable cell with another widget - Part 2?
The function you mentioned is used in Part 1. The solution you wanted is in Part 2. But try to understand Part 1. It allow allow you understand more about GtkTable.
By the way, to answer your question, GtkTable is a subclass of GtkContainer. However, interestingly, you do not have to remove a widget attached to a cell before attaching another one. What this means is that you can actually attach more than one widgets into the same cell! Try it. You will be amazed! For example, you can have a GtkLabel that spans from col 1 to 3, and another GtkLabel that spans from col 1 to 6, yet another from col 2 to 10. That is, you can have both overlapping and multiple widgets in and across different cells. Just remember to keep track of the pointer to each attached widget, and you will be able to remove them one by one and replace them with other widgets.