Why input voltage only appears over R1 and not R2?
Because the theoretical op-amp has infinite gain AND the non-inverting input is tied to 0 volts, the effect of negative feedback (R2) forces the inverting input to be at 0 volts.

Given that we assume gain to be infinite (in simple op-amp analysis) we can say (without much error) that the inverting input IS at 0 volts hence R1 connects to 0 volts hence all the input voltage is across R1.


  Since the input current is also equal to 0


The current into the op-amp inputs can be reasonably assumed to be zero but not the current taken through R1 - that current is Vin/R1.

You should think of the op-amp as a control system - the demand is set on the non-inverting input and the output HAS to swing to a voltage that forces the inverting input to produce a zero error. Maybe think of it like a servo system like this: -



Imagine the motor and position sensor were inside the op-amp. The op-amp output would be the output from the position sensor. This voltage is forced (due to negative feedback) to be the same voltage as the position demand (0 volts in reality). It makes no difference that there is an extra input (Vin); the inverting input voltage will be 0 volts and all the input voltage (Vin) appears across R1.