While it may be true that motorists must demonstrate some level of knowledge and proficiency once, in most states that's the end of it -- renewals are pretty much automatic. Even in states where there is some test required, it isn't generally a practical skills test. There's a big difference between knowing the law and practicing it. The evidence of this is the high number of drivers ticketed daily for offenses ranging from speeding to DUI to vehicular homicide. As with drivers, most people start out with at least some knowledge of bicycle law, even if it's just that they're expected to follow the same laws drivers are. The fact that there is no skills test required isn't that big a factor, in my opinion.

As far as the vehicles themselves are concerned, they may start out with standard safety features, but these can and often are neglected or intentionally removed over time. In some states vehicles must pass a safety inspection, but I know that at least some vehicles are modified just for the inspection and then unmodified immediately thereafter. Bicycles also come with standard safety features as required by state law. Again, these can be removed or modified. As above, I don't see a significant difference.

Just like driving, the risk at which you place yourself while on a bicycle is impacted significantly by the amount of training you've received, the way your bicycle is set up and maintained, and the way in which you operate your vehicle. Set your bike and yourself up for maximum visibility, follow the law, ride defensively, and your chances of not becoming a statistic significantly improve. You may still be hurt or killed through no fault of your own, but the same can happen in your car.