Guys, sorry to disappoint you, but there are only two possibilities:
1.) the london drug cartel spoiled the drinking water around SE headquarters with a ****load of LSD (accidently?)
2.) Some bastard hacked blogs.sonyericsson.com and spreads ****.
*sry, joking*
Seriously, who is this at SE that turns a whole company's concept upside-down?!
Very good news and the first time I suggest to buy another XPERIA phone!
edit: Did they perhaps recognize that their upcoming phones'll have a hard time around the competition due to hardware specs? I think it makes sense. Their flag ships don't look all that good (if you look at the hardware only!) and the XPERIA Play received some quite bad reviews out there. So to stand out from the crowd, they open the bootloader while every other company starts to lock it up. Only my suggestion.