This is a male Indigo Bunting - a beautiful bird. It is not a Blue Grosbeak for a few reasons, one of which is, as you mention, the lack of rufous wingbars (other reasons are a brighter shade of blue on Indigos, which are smaller...). However, you seem to have some (absolutely reasonable) confusion - the Blue Grosbeak isn't a finch. There ARE finches with the name grosbeak (Pine, Evening, Hooded...), but they are family Fringillidae. The Blue Grosbeak is in Cardinalidae, along with cardinals, New World buntings (including Indigo), and other grosbeaks including Rose-breasted, Black-headed, Yellow, etc.
English names can be quite confusing at times!