Voltage source and two resistors in series, voltage vetween Vs and R1
The voltage across R1 is the difference between the voltage at the top of the resistor and the voltage at the bottom or the resistor.  The voltage at the top is fixed to 10V because it is directly connected to the power supply (there is nothing in between for a voltage drop to develop over).  

The voltage between R1 and R2 is 10V - 3.3V or 6.7V.  If you calculate the voltage drop across R2 you will get a result of 6.7V confirming this result (the bottom is at 0V because it is the same node as the ground node of the power supply).

When you measure single node voltages in a simulation like this, they are always relative to ground.