I don't think there is any difference, but I don't know for certain. That's because getName() isn't implemented as you described. The Facebook profile record has a "name" field (as well as "first_name", "middle_name", and "last_name" fields). The getName() field gets its data from the "name" field returned from Facebook. I can only assume that Facebook implements it as you described.
Following up on my earlier comments: Facebook recently rewrote almost all of their documentation, updating it to reflect the current state of the platform. There were several places where the documentation was missing things (perhaps "middle_name" was one of those things) or even a few places that were completely incorrect. They announced at F8 Hack last week that all of the documentation had now been rewritten (with only a few small exceptions in cases where they intend to deprecate something), so there are likely a few more fields somewhere that Facebook sends back but that Spring Social Facebook doesn't capture or expose in its API binding. There may even be places where there are endpoints in Facebook's graph API that we're not exposing (I just discovered User/mutualfriends late last week). If you find any more of these, please let me know or open an issue in JIRA to request that they be added.
Craig Walls
Spring Social Project Lead