Basically, you pay the "fare" for the trip, then pay a surcharge for using an "express" train (the Shinkansen). It is the way it is. You can take any of other lines, but they will take longer and will be more "in-direct". If are not specific on what you want, they'll sell the "easiest" for the consumer. I have never been offered the Nozomi, it always seemed more money for little extra.