Good questions! The scotch comment always bothered me, too. Are the bottles shaped differently to tell the drinks apart? Color? I'm not sure how Ms. Houston knows the difference (I don't drink, so I wouldn't really know).

(1) As to why Columbo says no scotch - I think he examined a drinking glass when he first arrived at the scene? Maybe he recognized scotch in the glass and wanted to keep the bottle clean for prints? (But then, why not keep the entire set clean for prints?)

(2) Ice in the bin - Why is it there and who put it there? I'd say the answer is simple: "Because the script says so". However, I noticed something similar in "Prescription: Murder", when Columbo and Dr. Flemming go back to his office and Flemming offers him a drink; he, too, puts some ice in the glass. Yet, the bar and the ice have been there all day without melting???