Capt_Caveman is right. I got confused about your presentation of your network.

ARP requests is absolutely nessesary for the communication to work. When first connecting and starting up a network the ARP traffic is particulary high. On a network where nothing changes, no machinies are added or removed, the ARP traffic would decrease after a while. Don't know how it is with cache time on the ARP cache, but probably you would see a little ARP traffic even on a totally static network.

The amount of ARP traffic on a network is dependent upon several things:

1) Number of hosts on network
2) Size of arp cache/arp cache timeouts on host
3) WHO they talk to.
4) How often machines are rebooted.
5) Whether it is DHCP or static.

For a cable network, you generally have a LOT of hosts on the network, many of which are rebooted often, and using DHCP for IP Addresses. This means way more ARP traffic than, say, a static IP network of servers (where, in many cases, mac/ip pairings may be hard coded into the routers to avoid ARP delay).