Why can't I boot into recovery mode?
Edit: Apparently download and recovery modes are merged for the G1.  Just press Alt-L on your physical keyboard while in Download mode, and Recovery will show up.

What you're seeing is Download Mode.  The key combination is usually subtly different.  In the case of my phone, it's just a matter of having the phone connected to USB or not.  You should try it with and without USB, as well as removing the battery and doing a fresh boot.  (You can also remove the battery, plug into USB, and reinsert the battery and try).  Also try other keys -- you already know using Back instead gets you to that device info screen.