Comcast just told me that I would need to have their Internet gateway for Static IPs

Can someone tell me why I would need to have a RENTED Comcast Internet Gateway (which is another $10 a month) just to get static IPs assigned to my account? 

I am running a Cisco ASA 5505 with several other pieces of Cisco gear that are quite capable of supporting static IP addresses. This is really starting to get on my nerves with Comcast nickel and dimeing for everything.