First off, we need a shorter subject line for this one!
Secondly, I agree that lower end and mid-priced road bikes are 25% lighter than their counterparts from 1975.
Thirdly, I respectfully disagree with the contention that a modern top-end racing bike does not weigh 25% less than it's 1975 version. While it is clear that a top-end racing bike of 2005 is certainly much more expensive than it's counterpart in 1975 (even allowing for inflation), today's top-end bike is certainly lighter than the 17 lb figure mentioned by Garth Libre.
I own 20 or so on-topic road bikes. I only own 2 newer road bikes. My 2004 Cannondale R3000 weighs 16.5 lbs with pedals, bottle cages, and computer (but no bottles). It's a 58cm (not a small frame). I'm sure it would weigh less in a 52cm, and if I wanted I could build it up with lighter components and get it well under 16 lbs. Plus, Cannondale makes a higher end model that's even lighter. It's not uncommon for professional racing bikes to actually have weight ADDED (in the form of heavier components) to meet the UCI minimum weight of 6.8 kilos or 15 lbs (a regulation enforced ostensibly for safety on the assumption that too light is unsafe). Again I want to emphasize that the modern professional racing bike is much more expensive than it's 1975 counterpart. But it's worth pointing out that the 25% weight reduction figure is not far off for top-end bikes (19 lb x 75% = 14.25 lbs). If I have the $$$, I can go out tomorrow and choose between a number of complete road bikes that would weigh 14 or 14.5 lbs.
Of course, the next question that comes up is, "how long will a 14 lb bike last?"
A 19 lb steel frame bike can last indefinitely, provided you don't exceed the fatique threshold of the frame.
A 14 lb carbon fiber bike, on the other hand - who knows? I will say that carbon fiber is proving to be more resilient and longer lasting than some of it's critics would have you believe. And Titanium has a very long fatigue life. Consider this: my 16.5 lb Cannondale was made to be ridden by the pros in the most demanding races in the world. I will never have the physical ability to strain the frame to the same extent that most professionals will. If I put 5,000 to 7,000 miles a year on it, it should last for at least ten years. Of course, in fairness I should point out that my 1948 Hobbs of Barbican Supreme is still going strong after 56 years.
Something else worth mentioning: it's possible to add modern, very lightweight components to a steel frame, and have a complete bike that is lighter than 17 lbs. Perhaps eRichie or another steel meister can tell us how light they have seen one of their frames built up?
One other point that is well-taken is the change in how generations view product life. I'm 35. If my Cannondale lasts ten years, I'll be happy with that. My dad, who was born in 1923, would say ten years is not long enough for the amount I paid for that bike (about $3,500). Same applies to cars, etc. A few years ago, I flew (as a passenger) commercially on 727s that were made before I was born in 1969. The first house I bought was built in 1852. I value things that last, but I am in the minority in my generation. We have definitly created a "disposable" society. I believe bikes and bike parts are made to fail in a limited time so customers will need to plunk down coin for new/upgraded ones. But in all fairness to the bike industry, the same applies to auto tires, light bulbs, and many other things we buy every day. The technology exists to make a light bulb that will last ten years. Why aren't they widely available? Because they would put a serious dent in the profits of the light bulb manufacturers. I know, I'm starting to sound paranoid. But please, correct me if I'm wrong.
I ride just about every day, regardless of the weather. If I am racing or training for a race, I will ride my 2004 Cannondale (it's lighter and the STI shifting is a real advantage on all the small climbs we have around here). If instead I am trying to get in a hard workout I might ride the Cannondale, or I might just as well choose to ride my '71 Raleigh International fixed gear, as I did yesterday. If I want to go out and enjoy a long ride through the countryside, or do a charity century, I'll ride my '74 Jack Taylor, or '61 Carlton Flyer. The point is, the only time I'll choose the Cannodale over the others, is if I'm training to race it. Otherwise, I'm just as happy on any of my older bikes (sometimes happier). For those of you who haven't raced recently, a heavier bike would not necessarily hurt you in a USCF cat 3 or 4 race, but the lack of STI or Ergo shifting would definitly be a disadvantage, unless the course is perfectly flat (or a time trial, where many people still use shift levers on their aero- or tri-bars). I can shift to the right gear, every time, under load on a 15% grade with STI. Not one missed shift, or even a hesitation. Ever. I can not achieve the same reliability with downtube levers (even indexed ones).
So in conclusion, a reliable, top-end racing bike of today, meant to endure 20,000 or more hard miles over the course of a season (training miles are often done on dedicated training machine), can weigh as little as 15 lbs. This is almost 25% less than the 19 lb reliable, top-end racing bike of 1975. Maybe I should have put this paragraph first, and saved you the time of reading all the stuff in between!?!?
Duncan Granger thinking I'll ride a 1980s ten speed today in York, PA (where I work, not where I live)