Hi,
The function R2/(R1+R2) is a constant function, so this is a little unusual, but assuming that your transfer function is really:
Vo/Vi=(R2/Rs)*(1/(j*w*Rs*C)+1)
then the magnitude is:
(R2/Rs)*sqrt(1/(Rs^2*C^2*w^2)+1)
and we can see the factor:
sqrt(1/(Rs^2*C^2*w^2)+1)
as w gets higher and higher eventually becomes:
sqrt(1)
which of course equals 1, so we end up with:
|Vo/Vi|=R2/Rs=R2/(R1+R2)
At the cutoff frequency however the magnitude is:
(R2/Rs)*sqrt(2)=sqrt(2)*R2/(R1+R2)
and to reach within 1 percent of the final response we have to go to a frequency:
w=100/(sqrt(201)*Rs*C)
and then the response is:
1.01*(R2/(R1+R2))
but that requires a frequency that is:
w2=100/sqrt(201)
which is about 7 times higher than the cutoff frequency.
So yes it does approach that constant response, but only after a certain frequency has been reached.