HKEY_CLASSES_ROOT is combination of the "Software\Classes" subkeys of HKEY_LOCAL_MACHINE and HKEY_CURRENT_USER hives.
HKEY_CURRENT_USER is just a copy of one set under HKEY_USERS hive: [HKEY_USERS\S-1-5-xxxx]
Registry Healer scans both HKEY_LOCAL_MACHINE and HKEY_CURRENT_USER (or HKEY_USERS).