There is code in InnoDB (os/os0file.c) that limits InnoDB to one concurrent IO operation (read or write) per file. The code appears to be used for Windows and when HAVE_BROKEN_PREAD is defined. HAVE_BROKEN_PREAD appears to be defined for HPUX.
I can imagine that many Windows deployments won't mind or notice the impact this has on performance. But when you deploy on HPUX you likely have spent a bit of money to buy a high-performance server.
Have I read the code correctly? I don't build on Windows and HPUX, so I cannot confirm.
Does Percona do HPUX or Windows?