> * if your test suite has 100% coverage of arguments/return-value and field usage, you have type checked your program.

This is absolutely false. Others have pointed this out, but types are much more general than runtime checks in dynamically typed languages. For instance, you can check at compile-time that your program doesn't have data races or deadlocks:

http://www-kb.is.s.u-tokyo.ac.jp/~koba/typical/

Or design a library in Haskell to ensure file handles and other scarce resources are promptly reclaimed:

http://okmij.org/ftp/Haskell/regions.html#light-weight

Neither of these are testable in dynamically typed languages. Static types are much more powerful than dynamic types, in general.