The following link may be of interest. It does apply to the US market so I cannot confirm if the same is relevant to UK supplied cars.
www.volvoclub.org.uk/xc90recalls.shtml
I cannot offer any explanation as to Volvo's action in this instance, and from a PR point of view it does not seem the best approach. However, Volvo are Ford owned and I assume that their legal advisers would be giving them the correct action to follow to avoid any suggestion of liability, or otherwise. It would be easy for a good lawyer to argue that if Volvo showed the 'interest' that was suggested, then liability was being accepted prior to any actual cause being determined. I would also assume the insurance companies concerned will be making rigorous checks to see whether any liability is attributable to the manufacturer, or will they just pay out the money and 'close' the books?
The XC90 is not the only Volvo to have the battery in the boot, the S80, V70 and S60 have similar layouts, so the total number of vehicles with this system is extremely high. If the information given in one of the Posts that 2 fires were underbonnet and one was in the boot is correct, then that appears to make a common cause, apart from electrical, even less likely. I think we have all seen vehicles on the road that have been the subject of fire due to electrical issues, the only thing they may have in common was a short somewhere in the car wiring system.
This also not the first time that Watchdog have shown 'interest' in Volvo. They recently ran a feature on 'failure' of ETM systems in early S80 models. The actual parts were sourced from an outside contractor, as is normal for all manufacturers, and in this case were shared with Audi who also had similar 'problems'.
I agree that a manufacturer is responsible for the suppliers he/she uses and one assumes the parts have been tested thoroughly before being approved. The XC90 has been around for quite a while now so whether there is an inherent design fault, as was suggested, is still up for discussion. I am sure we will hear more in due course.