I used to think very similar to you. In recent years however, my position has begun to change. My husband and I have thought about moving to Italy. I wouldn't dream of moving there without knowing at least the basics of the language. This doesn't mean that I am going to be fluent though. Far from it. You need to actually speak the language to become familiar with it. I suspect as well that my family will speak English when speaking with eachother even out at a market place etc. It's easier for us to understand eachother quickly, without having to take time to "process" what is being said. English is second nature to us, while Italian will be something we elected to learn later in life and that does not come nearly as easy.

Step outside the box, look at these people that you encountered as individuals. How do you know they aren't citizens too? How do you know that some of them aren't purposely speaking in Spanish because they know that one or more of their fellow employees is having a hard time learning all there is to know about the English language?