This has annoyed me very much too. Using tab is not always desirable, for example when you're reading a large document. Tab could move away from where you were reading to the first link on the page.
I have found a work-around for the missing hotkey inspired by some of the answers from here: In Mac Chrome, how can I return focus from the address bar to the page?
Typing "javascript:" (without quotes) and then enter will move focus back to the page. OK, so that's one solution. That's however not very nice as you would have to do a lot of typing. Now what you can do is add a new search engine with a short keyword, like "u", and set the search string to be "javascript:". Then you can type in "u" and then enter to move focus back to the page without jumping around.
Edit: Apparently this still gets upvotes. If this really bothers you please let the chrome devs know here: http://code.google.com/p/chromium/issues/detail?id=92885