Why are there so many RJ45 serial pin-out options?

Good question!

RS232 pin-out standards exist for both DB9 and DB25 connectors, however there's no pinout standard for RS232 using RJ45 connectors. So console server vendors have adopted a variety of pin-out configurations (as can be seen from Zonker's Serial Signals Page on the conserver site). Serial appliance vendors likewise use a variety of RJ pin-out "standards" - so custom adaptors and cables are often required to interconnect with the serially managed servers, router, switches or power devices. 

Opengear's more recent products (ACM5000, ACM5500 and IM4200-X2) have standardized on the Cisco pin-out. Earlier console servers (CM4000) were designed with the RJ45 pinout used in Avocent's original Equinox brand console server.

Opengear's IM4200 family is available for the three most popular RJ45 pin-outs (X2=Cisco, X1=Avocent/Cyclades and X0=Avocent/Equinox). 

If you need to connect to a particular serial device or replace a competitor's console server an Opengear cable adaptor is generally available off-the-shelf.