To my understanding this is mostly driven by the twins themselves actually. I hear their internal dynamics are very special, and virtually impenetrable.
Sounds reasonable, don't peg it all on the parents, regardless. Kotowboy, I can't remember if you have any kids, but they get involved with dressing (and many other things) at a pretty young age. ...and as a parent you can be pretty surprised at what they want. My daughter considered animal pattern bibs a must have accessory when she was maybe around 1. Given looks, questions directed at us, and overheard comments, people didn't seem to consider she was choosing it, they seemed to assume we were paranoid about keeping her clothing clean. She also went through a long phase on wanting mismatched socks, and you get comments about being lazy dressers or too poor.
You can't peg everything on the parents. You'd have to be a lousy parent to never let them have any say in things.