Quite clearly, not everyone does speak English. In some (non-Anglophone) countries, many or most people that are directly employed by the tourist industry might speak some English, but even in countries where English is best spoken there are exceptions. (I have, for example, come across someone in the tourist information office in Uppsala who spoke virtually no English at all.)

I'd also contest that no one will be offended at anything. Certainly I do think it is rude to barge up to people in a non-English-language country and start talking at them in English without some sort of initial enquiry, somehow, as to whether they actually speak it (unless, of course, you know that they do).