Re: question about postgres storage management

The relevant bit that seems to describe fairly aptly why what you are suggesting is unlikely to turn out well:
  
"Some operating systems implement compression at the file system level. Files are typically divided into fixed-size blocks that are compressed into variable-size blocks, which easily leads into fragmentation. Every time something inside a block is modified, the whole block is recompressed before it is written to disk. These properties make this compression technique unsuitable for use in an update-intensive database system."