> "(ok, excluding numbers)"
That's a pretty big exclusion. There are times one really doesn't want type promotion from a particular number representation for performance or accuracy reasons, and if your dynamic typing system does not allow contracts to reject numerical types that will implicitly promote, you can run into huge performance problems.
An example: suppose you want to divide a list of numerators by a single denominator producing a new list. Each division is not guaranteed to produce an whole number. What's the type of the resulting list? What is the type of each member of the resulting list? What is the type of a sum of the resulting list? Is the per-division cost roughly constant or does it depend on the particular numerator, denominator pair?
Bear in mind not just differences between integer and real numbers, but that real numbers may be exact or inexact, and that there may be various representations of inexact numbers (from native floating point to various types of bigfloat).
Really strict typing -- whether in a dynamically typed language with contracts or similar mostly runtime mechanisms, or in a statically typed language with type checking at compile time -- forces you to deal with these questions explicitly. In this case, you might specify that the source list of divisors is a list of positive integers, and that each division produces a single floating point result (and thus you wind up with a list of floats; and you'd specify that the sum of the resulting list should be a float too). That sacrifices precision for performance, which will tend to matter depending on the content and length of the source list.
There are plenty of dynamically typed languages that get fiddly trying to avoid turning some or all of the operations into much more precise types than single float (or even doing exact representations, rational number style), and the performance impact can be dramatic.
Conversely, you may not want to lose precision as you move away from +-0.0f, so you may want to specify that exact arithmetic will be used in the operations in this example instead.