There's more to pseudonyms than legal reasons. What I write on the internet stays there, and I expect people to google my real name, but I do not wish to have all of my lives linked together.

For example, if I'd have to use my real name, I would never speculate. With a pseudonym, I feel comfortable making mistakes and tiny contributions. Similarly, if I were in a horde guild, I would not want alliance players to dismiss my civil politics opinions.