Yes its true it does have a remarkably strong roll cage. The problem THAT leaves; is that since there is VERY little for crumple zones (ones that absorb impact, thus minimizing the amount of energy YOU absorb) are quite minimal.
So yes, the likely hood of the car ripping to shreds in a serious accident are slim, the chance of suffering massive trauma from being whipped around like a pinball are significantly greater then that of even a miata.
Hopefully that answers any questions you may have
Per EPbrowns comments, yes the Smartcar is quite old in design. I remember a German co-worker showing me Germany's ebay website for all the smart cars as I believe the design is relatively unchanged from the very early 90's, minus engine improvements obviously.
you should google "Smart car - Roadster" to see their un-released European two door roadster. Its a very cool and sleak little car, I really wish they'd release it here