As a SoftLayer customer accumulates services they may accumulate usernames and passwords to those services. The SoftLayer_Account_Password data type stores a username and password combination for these services that are tied their customer account. This shouldn't be confused with username and password combinations for server-specific services.
For instance, an account's EVault WebCC information is kept in a SoftLayer_Account_Password record, but a server's root or control panel password isn't. Server software specific usernames and passwords are handled by the SoftLayer_Hardware_Software_Password data type.