As I understand the concepts, transferring tezos is one kind of contract. It has amount to move from account to another and the move is containing a transaction to track, that the operation gets through in meaningful time. So, actually tezos transfer is a small contract, sort of.
What about smart contract data types (is it amount of money in tezos, dollars, changing car to newer + some money,...) the options are unlimited, unless the Michelson language is and other blockchain rules are obeyed. Baking is the thing that makes it secure and I don't believe the type of data is in any role there.