[Spinoff of LUCENE-2308... we keep spinning things off... I feel like we live inside a particle accelerator]
Right now Lucene indexes the docTermFreq and positions into the postings, by default.
You can use omitTFAP to turn them both off, which if you also omit norms gives you "match only" scoring.
But, really, they ought to be separately controllable – one may want to include docTermFreq but not positions, to get full scoring for non-positional phrases.
Probably we should wait until
LUCENE-2308 is done, and make the API change on *FieldType.