Determining what should be an app in EA/APM has been more of an art than science for us. For ServiceNow specifically, we've chosen to lump ITSM, ITOM, ITAM, etc. into one entry "ServiceNow" which is a platform host. We then list APM, SPM, and a few others separately... for much the same reasons as @cbaser mentioned. APM/EA ownership is separate from SPM which is different from the "core platform". Not that ownership is a sole determining factor or anything...  So far (knocks on fake wood desk) this is working out for us.