It's normal to pronounce "GLU" as Glue, so people use the stylings interchangeably.
Glue Logic is a common thing in computers, not just macs, and it is, once again, also written as Glue by some people, GLU by others. Its the GLU(e) that holds everything together.
Apple does the same with DAV and DAVE (Digital Audio / Video I think?) - some documentation says DAV, some says DAVE.