Deltarpm xz problem with PPC generated rpms?

[Bill Nottingham]

Jonathan Dieter (jdieter at gmail.com) said: 
> He did bring up some other very good points, though.  Xz's compression
> output hasn't been set in sand, much less stone.  The file format will
> stay the same, but the same command-line options may result in different
> compressed files.

... in what way does he mean this? Obviously passing -1 ... -9 causes
different output, much like it does in gzip/bzip2/etc.

Bill