Security? or cheap cell processing?
I suspect this move isn't so much about security as it is about making sure that sony's very expensively produced Fat PS3s don't end up in parallel computing labs. It's always miffed sony that they sold at them at a loss and then didnt get the expected software boost when machines were used this way. There is little in the way of excuse to blame an alternative OS for quality issues if these were present when they first released the PS3.
No I suspect this draws a line under the issue and any fat ps3s that are updated effectively become tied to the sony moneymaking machine rather than ending up in a Lab.
Not that i am bothered. I didnt buy my PS3 to run linux, i bought it for the variety of gaming, media and connectivity it brought to my living room. Still going strong after two and a half years and the only console i actually still use daily. That Wii was a waste of money and the 360 is too noisy to use as a media centre (and doesn't have a whopper of a hard drive like i put in the PS3)
I am intrigued as to what the new firmware will actually give, but the removal of the alternate OS is no issue for me. I just hope they will natively support MKV, so i dont have to remux loads of stuff all the time ;)