About the vinyl, from what I understand, it was more of a wear issue and customer complaints that the industry shifted to mixed leather/vinyl combinations. For high end vehicle that are seldom driven, having full leather is fine. However, for a daily driver, the leather would wear extremely quickly in the "high traffic" areas of a seat.
So the cushion, head rests etc would remain fine while the seat bolsters would crack, split and dry out quicker. Hence the decisions to use a more durable product.
Remember, we are a minority here that really spend time taking care of vehicles. 99% of the people don't care, lack the knowledge to maintain true 100% leather. Even those that care, it can be a problem. I remember a girl on the board how drove a beautiful Audi TT (blue with very light beige leather interior) and in no time flat, jean marks where happening on her seats!