This is not the case for validation of XHTML result-documents. Here,
as Michael suggests, it is necessary to modify the schema. Are you
serious? Most of us can easily add templates to our styleheets, but it
is not a proper way forward in most use cases to open op schemas and
modify them just to do result-document validation.

I guess what you asking for here is that the original pre-validation
result is serialised rather than the post-validation result - this
would mean the defaulted values not present in your result would be
added for the validation and then discarded, leaving your
pre-validation result intact.  (much like when you just check a file
on disk for validity - it isn't left with defaulted values after
validation).

Its certainly raised an interesting question - should the serialised
version of the validated result be the per or post validation
instance?