That's not true at all. A lot of things listed have insanely long service lives precisely because the manufacturer doesn't want lawsuits
Seatpost: Al- 2 years. Almost infinite
Depends. Dissimilar metals can and have caused some problems, sometimes raising and lowering can start to score it some. It's good to be thinking about it in 2yrs time, but it may not require it. On the other hand, we've had to use some pretty extreme measures at the bike shop to remove seized posts...
I don't think I've ever had one last 4 years. The edges start to get torn away first, then either it starts to lose the integrity of the cushion, or the rails bend in a crash or impact. Possibly weakened by other crashes or impacts.
Front Derailleur: 2 years only if it doesn't work any more
Pivots wear, it gets sloppy etc. Mine currently doesn't really work all that well anymore, but at least I don't use it
Well, that depends. Shimano hollowtech? Ok, for the most part sure, but you may want to switch out the bearings to enduro-bearings after 2 years, which is cheap. Raceface/truvative's version of external BBs that still uses a taper-lock system? Take that on and off for two years (for cleaning, servicing suspension pivots, etc) and tell me it's still as solid as the day you bought it. In fact, my DH bike was suffering from this when I let it go. The cranks weren't "totaled", but they were "creaky" with a little play due to taking them on and off many times. Poor interface can do that, so it maybe depends here...
Pedals: 2 years bearings can be lubed and adjusted
True, and I find shimano bearings to last for just about forever, but on the bikes designed to take some hits, 2 years seems about right. I can usually make the better all-mountain/DH pedals last about this long until it's just not worth it to fix them (by replacing parts, cages, etc). It's about 2 years before they're just beat to hell bashing rocks and everything else. 2 years is infinitely better than the ~2 months I get on crank brother's pedals, haha, maybe they're shifting the normal distribution curve over to the left.
Frame: Al- 4 years
Ti- 5 years infinite
Steel- 7 years infinite
CF- 3 years
Yes, this one is odd, some things to think about though, impacts, dents, gouges, and so on. Most of these happen within "normal use", but can significantly degrade the life of a bike. The numbers above might correspond to some of that. Not only that, but some full suspension bikes are designed so poorly that the bearings give out, ovalize the holes, and make the entire bike worthless. This takes a few years to happen usually, and replacing the bearings helps, but especially for older bikes, they just weren't designed to go more than a few years with the poor suspension/pivots that they had, even with changing them out.
For the most part I agree, except for some of the really skinny-light XC stems out there that twist and flex significantly. I never really trusted those, even when new. There are still some of those out there, especially on older bikes.
Brakes: As soon as pads wear past mf's limit (durrr)
What......
Well, hopefully this is referring to changing the pads, although my avid BB7s lasted about 2 seasons before they were complete trash.
Headset: 1 year again why? relube or replace bearings
Yes, this one is odd. Headsets are not high stressed parts, not much reason to change it, unless it was like a $10 headset or something.
Fork: 2 years you can buy bushings and seals you know.....
Well, yes, but what about having to buy new dampers and other parts? My 1st generation Reba fell apart, it lasted into the 2nd season and by that time it wasn't worth it anymore. The older forks especially weren't really made to last more than a few seasons. Manitous, RSs, etc. Some of them have such poor lubrication systems that they are basically self-destructing as soon as you get them. The biggest exception are the old bombers with their oil bath system. Change out the gunky oil, slap new seals and bushings in, and you are usually good to go. Not really the rule though, more the exception. For some forks, when you are looking at ANYTHING else + bushings + oil changes + new seals + things like air spring seals, it gets expensive quickly, it might be better served by a newer fork, or at least a total tear down and rebuild (not where they just replace the oil, but where every seal, bushings, and wear parts are replaced). Lots of peolple worked the fox-crowns loose or creaky after a while, and those were expensive. Yes, there are some great exceptions, but I've got to say that the 2 year thing for forks isn't all that far off.
Wheels: 2 years cant service bearings or freehub?
With regular use, you are probably going to need at least a new freehub (no, you usually can't service the bearings inside of that), new bearings, possibly cones if it's a shimano, and if not you might run into the problem of the ever-increasing bearing receptacle, because of the forces worn bearings put on the races. I've never met a freehub I couldn't break, but the best for me has been DT, and about 2 years is my best. Then there's spoke tension, and everything else. If it's truly being ridden as advertised, 2 years is probably time to start thinking about the wheels. Every once and a while you're going to hit something and get an impact into the rim, eventually enough hits may have an effect. 2 years may not mean everything on the wheels is trashed, but I've had that happen before and chances are something needs to be addressed.
Stuff lasts a very long time if you take care of it.
Drew
Stuff lasts less when you ride more.