We should have put two and two together, huh? First, there was a software update (RC28) that was supposed to update G1's OTA immediately after launch. Second, there was a security flaw found in Android that definitely needed to be fixed. And finally, a T-Mobile G1 update showed up but in RC29 form.
Apparently, Google was in the mix of updating the software for G1 users when they identified the security flaw in Android's browser. Instead of updating all users to RC28 and then fixing the flaw in another software patch they decided to pull the update and rebuild the update. Thus, RC29. It's been released to users around 4PM Pacific Time, October 27th.
Thanks for your concern Google, I probably wouldn't have liked updating two days in a row anyway. Now where's my update? Anyone get the RC29 (or RC28) update?