I've ridden Rt 2 twice, from Chicago but I'm attracted to the area you took - maybe I'll do that next time.
I suspect the wider shoulders over the area are to aid in snow plowing. I don't think we'd bike up there in the winter, but they could plow the snow off the road and as it kept piling up it would get closer and closer to the actual driving parts. Having a wider area gives them a little hedge.
Actually, that may be possible. I used the gps for the majority of the trip so it recorded all track infomation. I would have to do some editing to connect the tracks, but the data is there. I'll post once that's all done, then I can possibly email you the data file.