It could be done with a single entity, but I don't see any reason not to still include linkshells for chat and I actually see it as a plus. I for one will utilize it as I have a small number of real life friends that also play. Whether we're in the same guild or not for running content or general guild chat, it's still nice to have a second chat channel to talk just to them and not the rest of the guild without dealing with a tangled mess of /tell.
It allows the flexibility of keeping in touch with several distinct friends groups while still maintaining loyalty to a main group. If you don't plan on multiple groups, no harm done, you just don't have to carry extra linkshells then.