Eureka! SometimeS one spots certain patterns, only to realise the pattern exists more widely (note the large number of verses beginning with a vav in our sedarot as an example, which is a phenomenon throughout much of the Torah).
Although in the verse above the instructions regarding the annulment of vows is given to Moses, in the opening verse it is the responsibility of the heads of the tribes. Moses is in charge of the transmission of the rules and the heads of the tribes then follow.
Some responsibilities are given to the entire nation, others are limited to a cadre (mitzvot for Cohanim, for example) and others pertain to different roles. In Mattot we have the soldiers, in Massei we have the princes apportioning the land and the Levite cities.
Is Judaism for everyone or for a select few? It depends on observance versus interpretation. Most mitzvot are for all. Judaism is individualistic in observance — people are to make their own choices and forge their connection with God. And all are encouraged and expected to further their Jewish learning.