*Spoiler!!!*
ok so this is my reason he looks like roxas
when you watch the movie where the heart goes or w/e its called you see that sora tells riku that his heart is aching. riku tells him that you should open your heart, so he does... thats when you see the part where ven's heart is traveling towards sora. Sora accepts him into his heart so now ven has a light to stay at. fast forward a bit. now were in KH1. Sora sacrifices himself and releases his heart to save kairi. in doing so he gets a nobody, with the fragment of ven in soras heart that was released too. so, ya sora's nobody should look like sora. i agree it should, but with that fragment of ven in his heart it changes on how the outlook of the nobody should look and now it looks like ven. i know that it is all opinions till theres facts, but thats why i believe he looks the way he does.