Pretty common practice to charge for map updates by vehicle manfs, not saying I like it but it is what it is.
You can skip a year, or two and some go longer on updates, I do not think you have to keep buying them to get one later on but not a bad idea to look into it.
I bought a vehicle that was 4 years old and never updated, then I just used the Garmin with lifetime updates instead and there were updates available, I would use the factory system as a reference at times.
I would not of bought the factory Nav but it came in the exact car I wanted which had a sunroof needed to help keep the dogs cool.