I am aware of that. But Potsdam was after the war in Europe was over and the Renner government had already been set up in Austria by the Soviets. The "percentage agreement" was an informal one between Churchill and Stalin and perhaps more an acceptance of the likely
status quo after the war, what with Soviet troops "liberating" most of the Balkans and central Europe. To my knowledge neither Roosevelt nor Truman signed on to this agreement. As for Greece, I'm not certain what motivated Stalin to "keep his word" (seeing as he failed to do so in Poland, Czechoslovakia, Hungary, etc) but perhaps it was the knowledge that Tito was supporting the communists there. In fact it was Tito's split from Stalin that caused a great rift among the communists in Greece and ultimately led to their loss in the civil war.
The fatal blow to the KKE and the DSE, however, was political, not military. In June of that year, the Soviet Union and its satellites broke off relations with Prime Minister Tito of Yugoslavia, who had been the KKE's strongest supporter since 1944. The KKE thus had to choose between their loyalty to Stalin and their relations with their closest and most important ally. Inevitably, after some internal conflict, the great majority of them, led by Zachariadis, chose Stalin. In January 1949 Vafiadis was accused of "Titoism" and removed from his political and military positions, being replaced by Zachariadis.
After a year of increasing acrimony, Tito closed down the Yugoslavian border to the guerrillas of DSE in July of 1949 and disbanded their camps inside Yugoslavia. The DSE could still operate from Albania, but to the DSE that was a poor alternative. The split with Tito set also off a witch-hunt for "Titoites" inside the Greek Communist Party, leading to disorganisation and demoralisation within the ranks of DSE and decline of support of KKE in urban areas.
At the same time, the National Army found a talented commander in the face of General Alexander Papagos. In August of 1949, Papagos launched a major counter-offensive against the DSE forces in northern Greece, code-named "Operation Torch". The plan was a major victory for the National Army and resulted in heavy losses for the DSE. The DSE army, could no longer able to sustain resistance in a set-piece battle. By September of 1949, most of its fighters had surrendered or escaped over the border into Albania. By the end of the month, the Albanian government, presumably with Soviet approval, announced to KKE that it would no longer allow the DSE to perform military operations from within Albanian territory. On October 16, Zachariadis announced a "temporary cease-fire to prevent the complete annihilation of Greece." That treaty marked the end of the Greek Civil War.
Source: Greek Civil War at AllExperts
It may also have been that Stalin was relatively satisfied with the "buffer" of client states that he had created, and simply did not want to oppose the British troops in Greece. It is safe to assume, however, that he would not have been disappointed had a communist regime come to power in Greece.
Back to the original comment, I still believe that if Stalin could have gotten away with it, he would have forced the Renner government on all of Austria and made Austria a Soviet satellite state.