Why the typecast in RB is broken
Because you can do things like this. Now c'mon! How often do you think tech support will get called by people who fall for this? IMHO, a "conversion operator" has nothing to do in a strongly typed language.
Dynamically typed languages like PHP? Sure! But if you have strong typing, all conversions should be explicit. If there are implicit conversions in some cases, but not in others, and the developer of an application can arbitrarily add new ones, you need documentation to help people through your project. And face it: How many programmers actually write comprehensible documentation, and how frequently is it outdated?
Self-documenting code is much better. Good programmers at least take care to write their code efficiently and cleanly, because the code is needed for the system to do what they're paid for. Nobody's ever going to see the programmers' documentation.