Why would a datasheet's typical application diagram vary so much from the layout guideline on the same datasheet?
There is a reason why datasheet has multiple sections and that is to give as much as details about their part. 

First page covers about its key features. Also they have added application circuit which is nothing but kind of schematic using their PWM BUCK converter. 

Now, when you are using SMPS in your design, you should give great attention to the layout techniques. that's why usually manufacturer recommends layout technique for their IC. main popular layout techniques are, 


Provide closure path from input capacitor GND to output capacitor GND for non isolated power converter design. 
Keep high di/dt and dv/dt regions smaller to the IC
Avoid routing sensitive signals under switching planes etc..


to help buyers, manufacturer added important layout technique and it should be followed most of the time. 

Now, lets come to SS/BST/Ton. Nothing is provided without any reason. there is a specific reason. you cannot keep open without connecting anything into it. 

SS is stands for soft start and most of the SMPS has this feature. User can connect an capacitor to limits its start-up inrush current and also to avoid overshoot at output during start-up. 

BST is stands for Bootstrap and it is needed for driving high side mosfet. it should be connected with a capacitor and some time diode as well to make the buck converter operational. 

TON is the special feature of this IC where they claims to keep constant on time always when the input voltage changes and eventually this helps to achieve faster transient response time of the converter. 

My advice would please read a lot of power converter techniques and then starts to implement. Just doing google wont help much without proper understanding or eager to learn something. good luck.