I want to thank you for telling about the Left Click and draw a box for zoom. I have been a Streets and Trips user since around 1997. The draw box has been the standard for most graphical programs like CAD and Document Management for years and was one of the desired features of S&T for years. I thought MS removed it and was really upset. Unlike the other user, I find the Draw and zoom considerably easier than any of the other options. The reason Google maps doesn't do it is because it can't. It is an internet application with limitation associated with internet applications.
Note that if you go to help, only the scroll wheel is discussed.
No, that's not why it doesn't exist in Google Maps. Internet apps have a lot of limitations, but this is not one of them. They didn't put it in, but that doesn't mean they can't put it in. (Distance measuring, for example, is one of the most useful tools in Streets & Trips. It's not in Google Maps, but that doesn't mean it's impossible. They just don't implement it. It's there in Microsoft Bing Maps.)
The help topic is called "Zoom in on a specific area," and it tells you to drag with the right mouse button. But as we all know, practically nobody reads the help -- other times, as in your case, some people read the help but can't find the page. The lack of feedback
in the UI is what's preventing people from discovering this feature.