you guys have no idea what you are talking about metal's. Titanium is not light as aluminum or strong as stainless steel. Titanium is approx 30% lighter than steel, but is MUCH stronger than any of the listed metals. Aluminum is fairly weak compared to any steel. Stainless steel isnt as strong as normal steel either. Only reason why aluminum is used is because it is lighter than steel. A one inch thick bar of titainum is strong as a 4" thick bar of aluminum or 3" thick bar of steel. Titanium is used because parts can be made so much thinner so they become lighter for the same strength as thick aluminum.
Basically its a difference of strength to weight ratio where titanium is far superior.