According to the OBi Device Administration Guide:
The maximum routing throughput between the WAN and the LAN side is approximately 30 Mbps. This speed can be achieved when there are no active calls in the system. Otherwise the throughput will be limited to a slower speed to accommodate the load for voice processing.
This is so disappointing these days when people can get 50-100Mbps with FiOS. I don't understand why 100Mbps switches are still around, can't be that 1Gbps chips are that much more expensive. Add a couple of dollars extra to the cost of the device and give me gigabit ports.
The ports are not the only thing to consider. CPU and memory are also tied to routing, so my guess the limitations are not the ports themselves but the overall hardware specs. I think the firewall is there for those who don't have any existing device. I highly doubt many of those people will be using 50/10 fios. If they are - well, they probably won't notice anyway.