You're right about the electricity point - replacement schedules are often dictated by power per watt, since improving that expands margins. If power is free or subsidized, hardware costs are a larger part of expenses and it becomes tempting to buy more older gear instead of less fancy stuff.

(As an aside, miners are a great place to buy computer parts for that reason - I've known several unloading last year's GPUs dirt cheap. The hardware is run into the ground, but I've seen "if it craps out call me and I'll replace it" deals.)