In the early days of MMOs, it wasn't really feasible for developers to put action-based combat into an online game and expect all users to be able to have a good experience. These days faster internet and other advancements allow games such as Age of Conan, Darkfall and Champions Online to have a combat system where, for example, dodging an attack actually involves moving yourself out of harms way. The alternative to this action combat style is the system that most MMO gamers of the last decade will be very familiar with, seen in games like World of Warcraft, Lord of the Rings Online and countless other titles.
MMOs without action-based combat still have their share of mechanics to keep things interesting. Abilities that must be used from the back or the side (or are more effective that way) mean that combat isn't necessarily a stationary affair, and you can still hit multiple targets in a lot of cases.