Pequeño universo... Me encontré con una herramienta que generaba esta sintaxis ayer y quedé bastante desconcertado.
Aparentemente,
FROM a
INNER JOIN b
INNER JOIN c ON (b.id = c.id)
ON (a.id = c.id)
es equivalente a una subconsulta anidada
FROM a
INNER JOIN (SELECT <<list of columns>>
FROM b
INNER JOIN c ON (b.id=c.id)) c
ON (a.id = c.id)