The as operator is not really the same as a conversion function. If the
expression is not of the specified datatype it usually returns null.
Number cannot be null, so I'd expect it to result in 0.
However, implicit coercion rules were added to the as operator in
ECMAScript 4 (and hence AS3)... but I'm not sure if String -> Number is
intended to be one of these?
I decided the best way to know was to write my own test...
var s:String = "5.20";
var n:Number = s as Number;
trace("n = " + n + "\n\n");
Prints:
n = 0
So, you must be seeing this occur in different scenario?