According to SQL Server Maintenance Solution - SQL Server Integrity Check, the SYSTEM_DATABASES
value includes only master, msdb, and model.
Why is TempDB excluded, when it too can have hardware issues causing page corruptions?
Interestingly enough, DBCC CheckDB FAQ: Check for Corruption in SQL Server by Kendra Little talks about the need to check TempDB but points to the Ola Hallengren script, which does not appear to be checking TempDB by default.