Here is a quick look at the 2013 Volvo C70. The doors and B-pillars have been reinforced in various ways. In a side impact the doors and B-pillars work together with the reinforced sills and a comprehensive system of cross-members and bulkheads to absorb the collision forces.
The C70 retractable hardtop also features a roll over protection structure (ROPS) with two pyrotechnically charged roll hoops hidden behind the rear seats that deploy under roll-over conditions whether the roof is retracted or not.
Take a look the screen shot from Moditech’s Crash Recovery System. Notice that the B-pillars don’t show any advanced or reinforced steel? Just remember, most convertibles have a very large B-pillar structure behind the sheet metal.