AS_NUMERIC and as.numeric - Could someone explain?

AS_NUMERIC in C more closely corresponds to as.double() in R

All that as.numeric() in R does is assure that the result is of a 
numeric mode.  It does not coerce integer variables to doubles.

Um... are you sure?? For the sake of lots of code I saw I hope you're 
wrong:

Check, for example,
str(as.numeric(1:100))

Yes:

 > str(as.double(1:10))
  num [1:10] 1 2 3 4 5 6 7 8 9 10
 > str(as.numeric(1:10))
  num [1:10] 1 2 3 4 5 6 7 8 9 10
 > str(1:10)
  int [1:10] 1 2 3 4 5 6 7 8 9 10

And moreover:

 > as.numeric
function (x, ...)
UseMethod("as.double")
<environment: namespace:base>

... admittedly I didn't answer the original question, but I suspect 
that the problem lies somewhere else ...

Simon