Aquarium Auto Doser - Is this Voltage Regulator Needed?

Hi guys this will be my very first Arduino project, but first I have a question regarding this setup though. Please keep in mind I am just in the process of learning about the whole arduino culture so I am still very green!
Why is the voltage regulator needed in this setup? The input for the arduino I will be using is 7-12v and where the RTC connects to the arduino is 5V anyway, is the voltage regulator really necessary? could you tell me if I am missing something?

Someone asked the same thing on the blog and the answer seems to be that it was to avoid having so solder wires into the jack.

The arduino can indeed accept 12V through the barrel jack although the on board regulator may get hot, so there is no real requirement to use an external regulator.

It indeed seems to be an unnecessary component .

The DS1307 needs 4.5 - 5.5 volts to work, you can't use 12v.
But if your arduino has a 5v regulator or 5v-pin, you could use that as well.

The schematic used is not like it should be by the way.
It mentions GND on pump 1,2, 3 and an Arduino-GND while all are simply GND.