Well, first off is the view with one resistor. We'll look at this with a car battery setup and say we've got negative ground and a +12v hot.
In our first circuit, we move 12 volts across 12 ohms of resistance and move 1 amp for 12 watts across our load. That is everything that can move there. The relative difference between the supply and receiving end is the same.
You could view this also as a +6v hot and -6v ground and the circuit would act exactly the same. Upping your supply (hot) or lowering your sink (ground) will create a difference in potential (voltage).
Now, let's change our load: two resistors of 6 ohms each. Our total resistance is now 12 ohms again, so we'll still draw 1 amp. Each load is now consuming half of that: 6 watts. To consume 6 watts across a 6 ohm resistor with 1 amp of power, you must lose 6 volts. Remember, current stays constant in a circuit wherever you measure it. That's why a fuse is effective anywhere in a series circuit. Remember that amperage is basically flow (gallons per minute), and the power derived is a combination of flow and pressure (voltage). Thus, voltage * amperage == watts (motive power).
So that's the electrical part. To use a water analogy, you have to think of the plumbing system a little bit differently. The "sink" where water flows to now has to be regarded as pressurized, so supplying some back-pressure. The loads are turbines in the pipe. If our supply is 100 psi and our sink is 50 psi, we'll get flow.
The pressure difference between two points on the pipe that is after the load is going to be negligibly small. It will still have pressure against the outside world, but the relative pressure when referenced against our 50 psi sink tank will be very low. Adding a split with lots of pipes after the last load won't change it.
If we put in a pipe before the first load and hook it up after the last load, we'll see 100 psi on it... or 50 psi relative to our two tanks. If we tap in the middle of those two equal turbines to our sink, we'll see 25 psi of pressure. The water had to expend some energy to get through the first turbine.
As long as we have enough pressure (voltage) to spin a turbine (drive a load), we will see a drop across that turbine equal to difference in pressure on either side. If we put multiple turbines in there, we'll see a pressure drop that is proportional to the amount of effort it took to spin the turbine.
Remember that voltage and pressure both relate to relative reference. After all, 0psi on the ground is usually measured relatively, and is actually 14.7 psi(absolute). So, pretend for a second that your supply circuit is +24v hot to a +12v ground, and it might possibly make more sense because you'll visualize some back pressure in your head and really focus on the fact that relative pressure is the driving point.
We create more power draw across our turbines by using bigger pipe and bigger turbines with the same pressure, or we can up the pressure on the current pipes. However, the pressure drop across our turbines will always remain in proportion as long as water can flow.