Apple was just as bad. :(
They switched at least 5 times in the early 2000s. Like you point out though they finally seemed to have calmed down.
MS had it in the bag too! Everyone wanted that 'sticker'. If you didnt have it almost no one would put your software on the shelf. To get that sticker you had to pass their usability tests that followed their style guide. Then they did like you said and switched it at least 2 times ever OS release.
Plus the web got in there and there were almost zero standards there. So we ended up with dozenes of framerworks that 'do it for you' and those have at least 3-5 generations of goop.
