Of course, just because the decisions came at same time does not mean the companies sat together and colluded. For instance Best Buy might have held a gun to their heads and forced them to impose such a policy, otherwise BB would stop carrying their products. In such a case the companies need not collude.
Irrespective of whether this action is enforced by Sony & Samsung or initiated by Best Buy, it is still anti-competitive. For that matter, even Apple's policy of enforcing a MSRP originally, was anti competitive. Even major designer houses have found it difficult to enforce a Minimum Price because it is anti competitive.
Why is this anti competitive? For the simple reason that it handicaps efficient retailers who can sell at lower prices and still make profits and protects the inefficient guys. Could potentially drive the efficient guys out of business by handicapping them this way.