You can have just the built in WAP but it is very limiting. Best way to explain it is consider the built-in is on par (or less) with retail grade AP and the MR is commercial grade. It's pretty much wifi on/off, broadcast SSID, and normal authoication like WEP, WPA, WPA2, and WPA2 Enterprise. If you are wanting splash screens, ACLs, etc then it's better to use MRs.
CMNO