I agree with you totally, however this isn't unique to Google at all - it represents a much wider lack of thought and care by UI designers across all kinds of software.
If UI designers thought about the points you make above as routine, then we'd end up better menus for sure.
The idea of a menu is fine, it is the implementation that needs work. They could easily fix this with two changes:
1) Add a button or link that is specific to exposing the menu (call it "Menu" or "Products" or "Go to other Google services" or whatever). This way it's obvious what the user must do to expose further options. That also frees the Google logo to simply link home, which is what logos generally do on the web.
2) Make the menu open and close with a click instead of hover. That way you don't have be an expert mouse pilot to get to the link you want. It also maintain consistency with the dominant paradigm in a GUI, which is "click to take an action." Think about it--have you EVER seen a hover menu built into an OS? I'm not familiar with Linux GUIs but on Windows and Mac OS X, menus always take a click to expose them.
If UI designers thought about the points you make above as routine, then we'd end up better menus for sure.