Well, it appears that the message has indeed been eliminated - although it has been replaced by another apparent attempt at humor. Peter Richard describes a Mac OS 7.6.1 startup crash (which initially appeared after installing an evaluation copy of DAVE, a Windows 95/NT client - although it is not clear that this is a cause) in which the following message appeared (instead of "Welcome to Mac OS"): "Just figured out what BETA stands for."
Just as with the Bluets message in 7.6, this message text is located in the DSAT #0 resource of the System file.
b. James Scott Williamson spotted unusable and unnamed check box in System Alert Volume box of Alerts window of Monitors & Sound control panel in 7.6.1.
[I have a few other even stranger reports, but I am waiting until I can replicate them or get other reports of them before I post them.]