That appeared to be the case when I did some experimenting yesterday but I can't replicate that problem today (and corrected my original post accordingly). So I must have been doing something wrong yesterday.
It seems that this implementation of text boxes- while different than how they did it in Pages '09- is just about as useful. However, I'm still experimenting...
I believe in Pages 09 when a text box was overflowed (full of text and then some), a new box could be created by clicking an overflow box on the (full) text box outline. I don't see that option here. Instead, you create a new text box, click one and the other to link them together, so 3 steps instead of 1. Maybe there's some more efficient way to create a new linked text box?
Yes, in Pages 4.x and earlier, a text box indicates that it is overfilled with a plus-sign at the bottom. To create a flow you click on the blue flag hanging off of the lower righthand side of the text box. The cursor shows it is loaded up with a plus-sign. You then click where on the page you want the continuation box inserted. They indicate they are linked with a blue line. They can be moved anywhere in the document and the link holds. Empty text boxes can also be linked, which is hugely useful for creating forms.