O2 have done this a number of times.
The original X10 was denied Gingerbread by O2 for ages.
My ARC was denied the ICS update from O2, so I simply installed a generic world ICS update over on XDA developers and oddly it works absolutely fine. In fact I got the latest ICS bug fix from Sony last week for it. Root it and then you can bin all the bloatware that comes with it.
I suspect O2 are just not interested in testing / updating to ICS due to the amount of work their guys need to do to "O2 it".