Personal modem with Comcast business and static IP

I've had Comcast residential gigabit with my own docsis modem for a while.  I'm switching to Comcast business to get a static IP.  The rep is telling me that I need to use (& pay for) a Comcast modem because I'm getting a static IP.  This just doesn't sound right as the static IP can be provisioned to my MAC just like the service is.    Unless it's just a tactic Comcast is using to force using their equipment.  Is the information the rep is giving me correct?  Very odd.