[avar]

Even with your edit this is worth replying to:

Why waste your money on a single rack-mounted PC when you can buy 40 cheap cellphones running Android and network them together. That'll probably provide greater reliability.

The obvious answer is the same as why some use mainframes over PCs. You can't easily convert all workloads running on a rack-mounted PC to a network of cellphones. Similarly, you can't easily convert all programs running on mainframes to running on PCs.

Which is what I was alluding to with the last paragraph in my upthread comment. There are mainframe use-cases that are genuinely entwined with those hardware platforms. A mainframe isn't just a fridge-sized PC.

[makomk]

The obvious answer is that a stack of cheap cellphones running Android is a pain to develop for, deploy and manage compared to something actually designed for server use. These are probably not areas where mainframes have the upper hand this century.