An SQLite database *is* a simple collection of one file in a well understood format. Accessible from other programs readily (SQL isn't that hard), including command line access via the relatively small sqlite3 binary. It falls down slightly on the "can't be edited with ed" test for text files, but apart from that it's an ideal choice for things like this. This really introducing some kind of opaque data format and it saves on having to write yet more code to parse text files that can be messed up by random editing (sqlite3 enforces sensible saving format to disk).
There are always going to be people who want text files only removed from their cold dead hands as a data format, but it's 2011 already and we collectively have a few decades of experience in how fragile text file editing can be (and well-known locations tend to be different locations even amongst different Linux distributions). This is a exceedingly minimal extra layer with some quite large benefits. I'm encouraged to see it happening more and more.