An incident took place in Mehoza - a non-Jew asked a Jew if he has wine to sell. After he is told no, he shoves his hand into a barrel of wine and mixes it and asks: Isn't this wine? -- what now is the status of that wine? Note the shofar-blowing to announce the issuance of a "p'sak din" - halakhic decision. To what extent has libation been involved in this kind of case? Moreover, note the different practices and the different levels of knowledge in various places - from Mehoza and Nehardea, and more. (All the cases brought in an attempt to refute Rava) Also, some of the sages were drinking wine, and the invite someone who later was determined to be a non-Jew. Other beverages, including beer, would have a different concerns (or none, as the case may be). If one sees wine, why would they suggest it was beer (maybe it's at night?). Also, note the difference between bishul akum, for example, and the issues here, which are from the Torah, and more concerned about idolatry than fraternizing.