Seriously. I write all my critical software in assembly so that my super-fast disks and networks aren't bottlenecked by unnecessary CPU instructions! Backup software always values speed over correctness!

You mean like rdiff-backup, which I've been using in production against millions of files for more than half a decade without a single problem?

It may be that some languages or runtimes host consistently more reliable software than others, but I'd bet that the individual programmer, coding style and practice have more of an effect on reliability.

How is that different from shell script which calls programs?