News Flash!: different operating systems use different platform UI standards!
In The GUI Gold Standard, Newsfactor asserts that "the GUI of certain operating systems seems to be determined not so much by general usability standards but by understanding the quirks and desires of its users."

I might point out that User-Centered Design says the "quirks and desires of users" matter. Although I seriously doubt that the reason Macintosh pull-down menus and the Windows taskbar are designed differently is due to some great variability in their user groups. The desire for innovation, lawsuits (fear of copying a good design exactly) and other factors are more likely reasons why there are few "gold standards."

"When Microsoft released Windows 2000, they were trying to achieve simplicity but they destroyed consistency," he said. "They've ensured that, from minute to minute, controls will disappear, and there will be a battle to learn where things are. They've asked users to spend a lot of time learning all over again."

Similarly, when Apple's GUI first came out, its range of icons made a great deal of sense, according to Benatan. But with many applications and a smaller range of icons, it becomes confusing.

Said Benatan, "The primary goal of a good GUI is: Don't make me feel stupid."