Also true - but if a client is demanding a shiny new unproven technology and is willing to pay for it then it's generally in management's best interest to oblige. That is what results in the younger developers being more valuable -- in school they've been able to dedicate considerable time to the shiny new tech before it was commercially viable. Now they're the only people with years of experience using it. If that's the only talent they have don't worry -- they'll stagnate once the next shiny tech comes along and their one value-add is moot.