Yep, direct and indirect; as you say, flatbar bikes (of all kinds, from full-on road race geometry to hybrid to mtb-framed to trekking etc.) are v. common on the roads not only in Europe but everywhere, and not only for commuting; the difference is that in North America there does seem a (tacit) assumption, absent in e.g. Europe, that 'real' cyclists (whoever they are??) ride drop-bar road bikes when on the road. I've never quite 'got' this assumption, and never will: to my mind, someone uncomfortably riding a full-on dropbar roadie, when he/she (age, body type, conditioning, primary riding conditions) might in fact be better off, and dare I say it actually a more efficient cyclist, on another type of bike, just doesn't make any sense -- but whatever. (Self)image, personal tastes, etc. of course have their effect in bike choice, just as with everything.