This is a distinction made by my father after I introduced him to socionics (with a bit of interpretation and reworking from myself). Socionics and MBTT are products of their respective environments. Notice how socionics comes from a country influenced by communism (indeed, it once was), and focuses on a theory of how humans help one another, whereas MBTT, which comes from a relatively individualistic, liberal society, focuses far more on the individual, and gives more concern for how that individual affects those around them rather than how they interact with those around them (which is what socionics is about). It's a very subtle distinction, almost imperceptible, but a distinction it is.
MBTT: the individual (singular) affects (others).
Socionics: people (a collective body) interact (with one another).
What do you reckon?