We used 'Save the Date' cards for our wedding for two reasons. 1) 90% of our guests were coming from far away (plane ride far) and 2) we got married in FL during spring break season and hotels & airfare were hard to come by...
We sent them out with hotel info so that people could get a head start. We also blocked off rooms at three different costs of hotels both to get better rates and to make sure there was enough loging available for our guests.
That said, to send a STD but not invite the person is horribly tacky. It's a pain to get the STD's with hotel info out in advance, so I can't see why anyone would do it unless they plan to invite those people.
In your case, my guess is that either the invite got lost in the mail or that they are sending them out in waves and yours is on the way (though, 2 weeks is a pretty big wave). I would absolutely ask the bride though - it's not like it's a secret party or anything. I'd be crushed if someone from far away wanted to attend my wedding and a stupid misunderstanding or a lost invite made that impossible. Ask her. You are breaking NO etiquette rules by doing so....