Anything safety critical should require a recall, and for everything else if the user isn't bothered that tells you a lot about how important updates to car software actually are.
I'd love to see statistics on how many injuries/deaths occur from recalled problems that users don't bother getting fixed.
I know I've had cars where certain defects (non-safety) were recalled, yet it took 2-3 weeks lead to get an appointment with the dealership, and several days in the shop once it was there (without a loaner vehicle). And I'm not talking full engine rebuilds either, just simple fixes. Most of the time I don't even bother anymore because it's such a hassle.
