In Stalin’s post-war speech, we saw how he used Soviet success in WWII to prove the superiority of the Soviet system. He argues that, despite the initial assertions of foreign governments and journalists, the Soviet Union is stronger and vastly superior to capitalist nations. It is hardly surprising that Stalin would use the opportunity of Soviet success and sacrifice in the battlefield to reassert the legitimacy of the Soviet government.
In my recent readings for my American Foreign Policy class, I noted that the U.S. also used its success in WWII to justify its own way of running the state. Both in the years leading up to and during WWII, FDR faced pressure from those both within and outside of his administration to take more authoritative control of the country. During the War, however, he rejected the notion that centrally controlled economies were more efficient than laissez-faire economies, which had been a popular belief during the Depression. Instead, he was careful to avoid excessive economic centralization. When Pendleton Herring was put in charge of writing the administrative history of the War, he concluded that the avoidance of any sense of autocratic rule might have made coordinating actions and policies more difficult, it nonetheless led to more than satisfactory results.
When Stalin gave his speech, it seems doubtful it was intended to convince foreign powers that Communism was more effective. The speech was more intended to simply bolster the spirits of the Soviet people.