since starbucks sells treif hot meat sandwiches, why should getting a coffee in starbucks be any different than getting coffee in mcdonalds”
The main difference is that when you go to McDonald’s it is NOT for the coffee. A Yid going to Starbucks is ONLY going for the coffee.
As to the question of cleaning the machines – as far as I know, coffee machines are not cleaned like cutlery or dishes. Though I could be mistaken, I believe there is a coffee cleaner that is run through the coffee machine. The only thing that makes the machine “dirty” is the accumulation of coffee oils. Running the coffee brewing cycle with vinegar in the machine, cleans it out completely. If there were ever a “hechsher” on the coffee served in Starbucks, it would have to be that only a kosher cleaning process was utilized. CRC, of course, has raised the relevant question, and it needs to be checked out.