Some loanwords like façade or café retain their accents.

Units like ° £ € and symbols like © ® × ÷ ½ aren't ASCII.

It doesn't take much to need one of these cases in a project.

That aside, the big problem with unicode is not those characters; they're a simple two-byte extension. They obey the simple bijective mapping of binary character <-> character on screen. Unicode doesn't. You have to deal with multiple code points representing one on-screen grapheme, which in turn may or may not translate into a single on-screen glyph. Also bi-directional text, or even vertical text (see the recent post about Mongolian script). Unicode is still probably one of the better solutions possible, but there's a reason you don't see it everywhere: it means not just updating to wide chars but having to deal with a text shaper, re-do your interfaces, and tons of other messy stuff. It's very easy for most people to look at that and ask why they'd bother if only a tiny percentage of users use, say, vertical text.

I see many uses of "pounds" or "GBP" on HN. Anyone with the symbol on the keyboard (British and Irish obviously, plus several other European countries) types £. When people use a phone keyboard, and a long-press or symbol view shows $, £ and €, they can choose £.

Danish people use ½ and § (and £). These keys are labelled on the standard Danish Windows keyboard.

There's plenty of scope for implementing enough Unicode to support most Latin-like languages without going as far as supporting vertical or RTL text.