you are right but apple shouldn't break hacked iphones they should just dellet the apps but not brick them.
For the most part, that is
exactly what's happening. Most people who installed 3rd party applications are still happily using their phones post-upgrade, but they may have temporarily lost access to their apps.
The people who ended up with bricked phones, mostly, were the ones who went further and modified their low-level boot ROM as part of the process of SIM-unlocking their phones. Physically, the boot ROM is a separate NOR Flash chip which is totally distinct from the 8GB or 4GB filesystem in which OSX and all the user level applications reside. The boot ROM is the chip which contains the low-level instructions executed by the ARM CPU in the first few nanoseconds after the chip powers up and before it knows about any of the higher-level stuff like drivers to work with NAND flash.
Now think about it... Among other things, the boot ROM contains the bootloading software which is used when the rest of the phone's software is being updated. If you modify the boot ROM in ways that Apple wasn't expecting, then that bootloading software might not function the way in which it was originally intended. Therefore you may disrupt the process of updating your software, and end up with a corrupted upgrade and a useless phone.
Nothing too far-fetched or evil about that.