Mismatch between v$filestat and v$sysstat

Why doesn't sum(phyrds) from v$filestat match 'physical reads' from v$sysstat?

SQL>select sum(phyrds) from v$filestat;

  SUM(PHYRDS)
-------------
    9,674,425

SQL>select value from v$sysstat where statistic# = (select statistic# from 
v$statname where name = 'physical reads');

       VALUE
------------
  56,952,459

Version and OS doesn't seem to matter since I've gotten similar results on 
multiple configurations (8.0.6, 8.1.7.3, 9.2.0.6, HPUX and Windows).  I figure 
I'm just having a brain fart and forgetting an obvious ingredient to the 
formula.  Any ideas?

Thanks,
Brandon

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