This isn't entirely accurate. The rule for Cisco APs to turn on Protection Mode (use of RTS/CTS or CTS-to-Self) is:
If the AP is required to respond to a probe request with a probe response, then protection mode is automatically enabled. To prevent this from happening, simply disable broadcasting the SSID in beacons - which, btw, also disables probe responses when probe requests contain the "broadcast" SSID (which is blank (or null)). The 802.11 standard says that APs are required to respond to probe requests from any station that sends one with the broadcast SSID or the SSID of the AP. Since you would have implemented it such that the AP won't respond to null SSID fields in the probe request, the AP won't have to turn on Protection Mode (which will cost you half of your throughput in an 802.11g environment). Also, any 802.11b associated clients on an 802.11g AP will enable protection mode. Cisco has Association ACLs to prevent accidental associations.