Two things:1) Plasma is still subject to gravity, and still retains some fluidlike properties, just as both gases and liquids are subject to the principles of fluid dynamics.
1) Plasma (as in the Sun) interacts with magnetic fields, whereas gas (as in Jupiter) does not. The source of the plasma (fusion in the case of the sun, but solar wind in the case of our ionosphere, and gravitational acceleration in the case of accretion discs) doesn't matter.
2) An isotropic force plus an anisotropic force must have a net anisotropic effect. Therefore, if we know that an anisotropic force is in effect, there must be another anisotropic force to counterbalance it in order to have an overall isotropic equilibrium.
2) Of course, the Sun is not perfectly spherical, just really close. There is still a bit of equatorial bulge, the result of the anisotropic force you spoke of, but MOSTLY it is cancelled by fusion pressure, or the Sun would be more oblate.