Not necessarily. For one thing, having a program which makes web requests is not always a problem if, for example, it comes with an improved interface or other features that benefit from a local program. It could, for example, cache translation results and store them in a convenient local file which some users might value.
For another thing, Google Translate does work offline, but only on phones. You can download offline translation databases which work when the phone is disconnected, though I think the quality is probably different when not using the server's presumably much larger ones. Someone who knew that might expect there to be a desktop application using the same files for offline translation, and if anyone from Google (or a different company with translation software) is reading this, I'd like that, please.