Service sustainability

When Steve Hitchcock says that "sustainability must precede preservation for institutional repositories," what does he mean?

Not to put words in Steve's mouth (Steve has plenty of words, all well-chosen), but here's my one-sentence take on it:

A service is sustainable as long as it has a constituency both willing to fight to keep it going and able to make that fight count.

This is, I grant you, a somewhat cynical assessment; I welcome less cynical ones in the comments. The corollaries for nascent data-curation efforts I leave to readers.