Google allows pseudonyms on almost all of their other services, which are supposedly getting integrated with Google+. How is that supposed to happen, exactly?
Twitter isn't primarily for alternate personas. Where did you get that idea?
Futhermore, what makes you think pseudonyms are for just for alternate personas? There are plenty of legitimate reasons for people to be using pseudonyms, both online and offline.
Many people are known only by their pseudonym (even when not online). How are their friends supposed to find them on a social network where they're only allowed to use their "real name"?
To quote you: "I want to call people by the same name we use in person."