How many software systems are even 1% as battle tested as a "CPU"? Even the most well designed software system doesn't have the kind of test coverage of a hardware.
CPU's are complex and far from perfect, often shipping with hundreds of 'errata' at the design level plus a wide assortment of random manufacturing errors in each chip. So, there is software that has fewer bugs and better coverage than a modern CPU. ex: Grep
EX: Pages 19-73 with 2 to 4 errata per page for a single popular CPU design: http://download.intel.com/design/processor/specupdt/320836.p... And that's just limited to stuff Intel knows about.