CAS simplifying non-zero expressions to 0

[parisse]

Nigel, I confirm I can easily modify solve to solve your equation (will work for linear equations).
Nick, here is a way to "simplify" your absolute value
z:=1/(1/r+1/i/w/La+1/(1/i/w/Cc+1/(i*w*Cr+1/i/w/Lr)));
z2:=factor(z*conj(z));
If you want the coefficients of w of the denominator of z2: d:=symb2poly(denom(z2),w). There you can subst the value of r, etc. with numeric values. For back evaluation at some value of w, you can use horner(d,value).
I think that the main misunderstanding is about simplify : simplify is probably a bad CAS commandname, because there is no way to guess what the user means by simplification.
I hope you will reconsider your opinion about Xcas and the Prime CAS...