Hi,
The flexichain .asd file includes an almost-useless package: there are no persistent definitions other than the system itself, so (since asdf arranges for the file to be loaded in a temporary package which uses the ASDF package) there's no need to define and use a -system package. (Packages are surprisingly heavyweight objects, which is why I'm drawing this to your attention).
There's one way in which having a package definition can be useful -- for incremental development of the .asd file itself. However, you can achieve that, if this is one of your goals, with an explicit asdf: prefix to the defsystem symbol.
Cheers,
Christophe
[ PS: I'm not subscribed to this list, so Cc me if you want more discussion on this point. ]