QUESTION: The Gemara relates that Rava, during a single meal, would recite a Berachah Rishonah on the wine of Kidush and also on the wine of Birkas ha'Mazon (Rashbam). To defend his conduct he cited the practice of the house of the Reish Galusa, where the practice was to recite a second blessing on the wine of Birkas ha'Mazon. Rav Yakov bar Ada argued that the practice in the house of the Reish Galusa is no proof, because a person in the house of the Reish Galusa never knew if he would get any more wine to drink, and therefore he recited a new Berachah every time more wine was served.
What is Rav Yakov bar Ada's logic? Why should the guests of the Reish Galusa recite additional blessings just because they are unsure whether or not they will be served more wine? On the contrary, since they do not know what else will be served, they should have in mind at the time of their first Berachah that they will drink whatever the host serves, as the Gemara in Berachos (42a) says (see Rashi there, DH a'Taka d'Reish Galusa).
(a) TOSFOS (DH Lo Havi) explains that the people in the house of the Reish Galusa recited a new Berachah only on the cup of wine used for Birkas ha'Mazon. Since so many people were present there, each person thought that he would not receive any of the wine. Therefore, one who did receive some of the wine of Birkas ha'Mazon needed to recite a new Berachah. Other wine served during the meal was covered by the first Berachah, because everyone had in mind to drink whatever the host served (as the Gemara in Berachos says).
(b) The RASHBAM (DH Lo Havi) implies that in the Reish Galusa's house, they recited a Berachah on every cup of wine, even wine served during the meal. Why did they do that?
TOSFOS RABEINU PERETZ mentions that there were a large number of people at the Reish Galusa's house, and the amount of wine that was normally served did not suffice for everyone. When each person recited the Berachah on the first cup of wine, he did not have in mind that there would be any more wine for him to drink. Therefore, he was required to recite a new Berachah on every new, unexpected cup.