Yes, both are specified as zero or more in the DTD. Ideally, if you
include multiple desc/review elements in your data an application
would "do the right thing" and choose the most appropriate based on
specified language, for example.
I've just added a lang attr for <review> to the DTD - thanks for
pointing out this oversight. Additionally, the core XMLTV.pm module
may not be in sync with the XMLTV DTD for some of the newer elements
but should always output valid data nonetheless.

I hope this helps to answer some of your questions - please follow up
with any more on the xmltv-dev list.

Cheers,
Nick