Don't worry, GM didn't go willingly.
The National Highway Transportation Safety Association FORCED GM to recall the vehicles.
http://biz.yahoo.com/ap/040112/na_fi..._recall_4.html
GM has known about the problem for quite some time but was in full denial mode that there was even a problem. Only when the gov't forced them to take action did they.
It doesn't matter how old the cars are, when it comes to the public safety, GM has an obligation to ensure that the cars that they build are at least safe and this obligation outweighs any warrantee written or otherwise implied.
To all you anti government types out there, this is the kind of thing that demonstrates the effectiveness of government regulation in industry.
GM wouldn't "willingly" recall anything. Even if its cars were exploding half they time they were starting up, GM wouldn't recall them unless they were forced to.