The data entered into a Web Form is saved as an XML file, and that XML file conforms to the structure defined in the XSD of the Web Form; in other words it has the type defined in the XSD.
That XML instance document happens to be stored in the repository with a DM style content type as well, but that behaviour is best thought of as an internal implementation detail and is not readily customisable. With WCM it's better to think of "types" as being defined by XSDs - the DM style mechanisms (aspects, types, etc.) are (to simplify somewhat) not relevant in WCM.
Cheers,
Peter