Titanium frames do fail, largely because the welding requirements are so much more rigorous than for steel frames. So I would take the "lifetime" bit with a large grain of salt.

On the other hand, I've owned a steel frame for 25 years that was used, abused, rode hard and put away wet a gazillion times...And it never failed. Right now I also have a steel frame (much more modern, thin-walled tubes) which will soon celebrate it's 20th birthday...It, too, has been ridden a lot - about 45k miles - and not babied at all. Still going strong.