I think if you are using gravity all the way there is no need to have a pump. Only a hose to fill the HLT at the top.
In my case I use a hybrid gravity single-tier batch-sparge system.
The point is that I used to use a pump but found it kinda troublesome and messy. I can cool my wort just as well without a recirc or whirlpool. Less equipment and fittings to buy, clean, maintain and keep track of. To get all the connects, fittings and silicon hose I wanted was going to run me over $100!
I've pretty much eliminated everything from my brewery as non-essential and have streamlined my process. I use a minimum of equipment and do large boils (12+) on my kitchen stove. No tricked out system. Just a kettle with a ball-valve, a 70qt cooler, several large buckets, one piece of vinyl tubing and a single long handled spoon. A copper IC and frozen bottles to cool it all.
So I'd say one would have to consider the expense and impact a pump will have on the process, the system and the learning curve. Mistakes will be made. A flailing hose pumping hot wort is no walk in the park... And like many things in homebrewing just because everyone is doing it and it seems like a natural evolution to the process doesn't make buying a pump necessary.