Keep in mind, that most people who race will ride their bikes about 12,000 to 15,000 miles a year, so if a leather strap will only last a season of that kind of riding then in the real world where most only ride about 3,500 miles a year and put less stress on the straps, a leather strap will last at least 4 years, and the laminated ones much longer that's why your laminated ones could last 15 years.

Personally I would not buy the Brooks leather straps, I like their saddles and they will last far longer then regular saddles, but a leather strap is a leather strap and the Brooks $50 strap won't last any longer then a regular leather strap that cost $20. But the laminated ones like the one at Velo Orange should last a great deal longer.