Depends on the level of specialization. A highly skilled engineer working on compression, cryptography, data stores, operating systems, compilers, etc... (the

Depends on the level of specialization. A highly skilled engineer working on compression, cryptography, data stores, operating systems, compilers, etc... (the building blocks for other systems), cannot be treated as commodities today. Highly productive engineers with regular skills, might not be easily replaceable either, it might just not make financial sense for your company. Engineers with regular skills and regular productivity can be replaced. But abusing this might have effects on the culture.