http://www.whatwg.org/specs/web-apps/current-work/#values
In the microdata spec, the values of itemprops are defined for certain elements, and there is, at the end, a catch-all for undefined elements to use the text value. However, there are some elements that have values in the DOM but no text values- specifically, input, textarea, and select.
I've come across a use case recently where it'd be useful to be able to define textboxes as properties - using a microdata-to-JSON parser to submit a form in JSON mode using Ajax, and then deserializing it on the server. Though this specific case may be a bit of an edge case, the intended use for Microdata is to define a machine-readable structure. Excluding these- or any- element seems like an oversight.
Does anyone have any clarification on why they're not included (for example, am I looking at it too generically?) or have any comments?