Why FIN, ACK instead of just FIN

Hi,

 

Probably easy one, but can't understand this flow based on what I can find on the web about connection tear down.

 

Here is TCP flow

 

 

I can't understand why packets containing FIN, ACK are used. In docs I was reading tear down is pictured like that:

 

 

I understand that sequence FIN, ACK can be used to both confirm reception of previous packet and initiating tear down but what packet is confirmed by line highlighted with blue (to be honest I can't see which packet is confirmed even in first FIN, ACK packet in the flow - initiated server side). Or my reference picture is from some old times and now most often tear down is using FIN, ACK sequence as default?

 

Piotr