(edit: not sure about the ISP in question, but my company also provides the software interface so you can port forward, parental controls, etc etc). So there are costs involved especially when people need to call our techs on the phone to figure out how something works.
Yeah, I’m going to back up the idea that the service charge comes with the tech support if your wireless ever stops working. If you get your own modem or router that has wireless capabilities, if anything ever goes wrong with it (happens often with wifi stuff), don’t call your ISP because they will ask if your modem is connected directly to your computer or if it is going into another router, or what. Basically, you’re paying for more peace of mind and more tech support. Not entirely unjustified.
Frankly, I don’t think it’s worth paying extra for. But I also don’t mind troubleshooting these issues when they come up.
There are wired hubs and switches. You could have lots of machines on a wired connection as well.
Legally speaking, your ISP can restrict your use of their signal- including prohibiting use of your own wireless router- but almost certainly doesn’t. So yeah, call them and tell them you didn’t ask for a wireless modem.