That's only to back up TA upgrading with root from 4.2.2 is to 4.3 or 4.4 is not supported.
Upgrade to stock then unlock
Also I think losing all data is a sacrifice worth it besidesvyou can back up data Sony provides you with the tools or just copy SD card to desktop and restore when done.
OOORRRRRRRR.....
You can get pre-rooted firmware here
http://xdaforums.com/showthread.php?t=2711982
Backup TA and unlock(if you want but I'm getting the sense that you just want root)
The last option is the preferred one no downgrade pain nonsense.
And finally to answer your Question: Sony is gonna Sony they say they don't mind you unlocking boot loader but the remove the good stuff like BIONZ. Now just imagine with root in which they never claimed to not mind about.
yup owns Z1 and stuff.