Age is not the only consideration when talking about rubber getting harder or brittle. You also need to consider factors such as composition of the rubber, ultraviolet light and the atmosphere the tire is stored in as well.
I realize that you have a lot of racing experience from your signature and my "load of crap" comment was not directed towards you but the local shops that spew this garbage. I would however I'd like to know how you think the system works?
Unless motorcycle distributing goes against the standard way business is done in this country, the following guidelines come into play. When you buy a product for resale, the larger quantity you buy, the better the multiplier (deeper the discount). Over time, your discount level can be enhanced further by issuing blanket orders (large order that is broken up into multiple deliveries) that gives the supplier an idea of your longer term purchases. This gives you a deeper discount due to the fact that you are stabilizing the suppliers business by guaranteeing sales over a period of time.
There is no way that my local Yamaha
shop buys anywhere near the volume of tires or aftermarket accessories that Chaparral, Rocky Mountain, etc. does in a year. Because of this, the local shop is buying these products at for the same price that the larger places sell to the public. I've seen this and discussed it with one local shop that I used to buy bikes from for years.
I've seen tires in my local shop with so much dust on them they'd need cleaned before installing them on the bike. According to your theory, these tires have to be better than what I'd get from mail order.
I'd be a lot more worried about the small, local shop buying out of date tires for resale because they are trying to compete in a low margin market.
My complaint is not with all shops and I agree with you that once you find a good dealer, it's worth a little extra money to get service and the knowledge they can supply. I live 65 miles North of Denver and I mail order parts from a shop there. Sounds stupid when I could get the parts locally. Why do I do this? They give me great service, on time delivery, tons of free advice and I've known the owner for years. I used to live close by and bought everything I could there because of service. He gives me a discount that makes his prices very competetive with the larger mail order places.