I think the others do have lines, but aren't neccessarily concentrating on Runway looks and doing more ready-to-wear.
Mycheal KNight has a website http://www.mychaelknight.com/home.html
Chris March http://www.chrismarchdesign.com/ I don't think he was that interested in having a fashion line.. He enjoys making costumes, but I think he has designed some stuff for celebrities at their request.
At the reunion show, Emilio asked why he didn't win and they felt he had a 'line' not a collection. Collections are supposed to be avant garde, 'wow', and over the top. Lines are more wearable - beautiful, but not always 'wow'. If he had more pieces like that evening dress, he might've won.
The final 3 were the strongest from the beginning. As much as I thought Mila's pre-runway work was boring, she got the look together for the runway show. Seth definitely has a look, but not one that i'd wear.