Pre-CANBUS cars were even easier to exploit. Much of everything on those systems were in plaintext, and could be easily tinkered with. A 25 year old car may have many of the same safety systems (although it is definitely missing a few), but the passive safety systems that do exist are most certainly not to the same standard as today's vehicles. To put it plainly, you are way more likely to die because the safety cage collapses on your late 90's vehicle, than you are to die because someone attacked the CANBUS of your vehicle.

DEFCON has a lot of great security demos, but don't mistake any of those demos as representative of the real-world landscape of issues.