That file is the crappy "patch" version that tries to patch you from RC29 to RC30.
Here is the full update, which should be much more reliable
Obviously, don't install it unless you want to lose root access
Update for those who are interested: I went ahead and bought myself a new G1. One of the stores in the area had a couple. It still had RC28 (not RC29) on it, so I'm back in business. I'll just unlock my RC30 one and sell it on ebay.