I know different things are important to me when viewing programming text than reading. A simple, somewhat contrived example would be whether 'r' and 'n' together are easily discernible as 'rn' or 'm' (which is mostly a non-problem with mon-spaced fonts). When reading text, I can infer from context what the word most likely should be, but when programming, that's an error waiting to be found at some point.
To expand on this, different programming languages may stress different qualities of a font. From experience, I find when parenthesis look like curly braces in a font, it increases my frustration as it causes ambiguity where there should be none. This may be less of a problem in a language that uses fewer braces.