There's not a single Google index; rather, it spans multiple tiers. Perhaps those pages fell through the cracks, in the figurative sense -- perhaps there is not enough capacity in the tier(s) they are in and the cutoff is too aggressive. There are internal tools to debug this, but of course nobody that has access to them will report here.

Uh, five minutes after I first tried, now the review is the first hit for [lou reed "rock n roll animal" tim bray] and a bunch of variations. Enough people searching for it might have changed the state of the system.