Several users at http://moodle.org/mod/forum/discuss.php?d=166860 reported buggy behaviour of Workshop 1.9 > 2.0 upgrade code. During the code review, a bug was detected in workshop_upgrade_module_instances() function. It tries to update the instance value in course_modules. But it is not able to detect whether the current instance value mean newid or oldid so it can link multiple course_module records to single workshop instance.
Because there is no easy way how to keep an information on which course_module record already contains newid, it was decided to use import_record() that preserves record's id when migrating workshop instances from workshop_old to workshop table.