Projected rotational velocities (vsini) have been measured for B stars in a sample of dense, bound clusters as well as low density, unbound OB associations. In comparison with stars populating unbound associations, the mean rotation speeds among stars formed in bound clusters are higher, primarily because the cluster population lacks the large cohort of slow (v sini < 50 km/sec) stars found among the associations. We argue that the pattern of rotation speeds that differentiate B stars in bound clusters from unbound associations is likely imprinted during the star formation process. The observed difference in N(vsini) between clusters and associations finds natural explanation (1) if B stars are assembled in the same way as their lower mass analogs: via magnetospherically-mediated accretion; (2) that during the stellar assembly phases, stellar rotation speeds are fixed by the angular rotation velocity of the circumstellar accretion disk at a radius, rX, where the stellar magnetosphere and disk are linked and forced to co-rotate; (3) that rX is smaller in regions where the time-averaged mass accretion rate through circumstellar disks is typically higher; and (4) that the parent molecular clouds that give birth to dense clusters have higher turbulent speeds, and as a consequence, higher time-averaged accretion rates during the stellar assembly phase.