survival::survfit,plot.survfit

plot(survfit(fit)) should plot the survival-function for x=0 or 
equivalently beta'=0. This curve is independent of any covariates.

This is not correct.  It plots the curve for a hypothetical subject with x= 
mean of each covariate.  
  This is NOT the "average survival" of the data set.  Imagine a cohort made up 
of 60 year old men and their 10 year old grandsons: the expected survival of 
this cohort does not look that for a 35 year old male.
  
  	Terry T