iPhone upgraded/updated to v1.1.3 can't be downgraded...?

It's said that when you update your Apple iPhone to firmware version 1.1.3, you would not be able to downgrade back to previous versions (v1.1.1 and v1.1.2). According to Nate, downgrading from v1.1.3 would brick your iPhone.

"If your iPhone has never been unlocked, downgrading from 1.1.3 will leave you bricked until you upgrade back to 1.1.3, as far as I can tell. The phone (even with an authentic AT&T SIM) reports an Incorrect SIM while iTunes says there's no SIM at all, when you've downgraded back to 1.1.1 or 1.1.2 (1.0.x untested). If your phone was unlocked, the baseband upgrade fails on 1.1.3, so you will not have this problem but will not get 1.1.3 to work. "

Note: The firmware version v1.1.3 has not been officially released by Apple yet.