Hmm, of course, but those announcements are not specially directed to Americans or British people. As far as I can remember, things like those announcements started with EU, at least in Germany. Fact is, that English is World Language No.1. Most pupils in EU learn English as their first foreign language in school, don't they?
It makes some sense to have kind of common language I guess, at least it makes things easier. Maybe Esperanto or something like that would be the better choice, don't know. Anyway, how could they decide there in US for an announcement in another language? For which language? Would be quite exhausting listening to an announcement in any language.
Apart from that, travellers from US or GB and even (pitiable) Call Center Agents often ask when they start: Do you speak English? At least that's my experience.