Literacy has never been a single monolithic skill. It involves both reading and writing, and these two skills are independent of each other. More to the point, literacy involves reading and writing differently in a range of situations. You may consider yourself literate because you have read Shakespeare, or because you can write a coherent quarterly report. But you don't write your quarterly report as a sonnet. Different forms of literacy apply at different times, and people can be good at some kinds of literacy while needing assistance in others.
Basic decoding (reading) and writing are rarely the problem in these misunderstandings. While many comments left by strangers on the threads I have studied are misspelled, use bad grammar, or are written in all-caps (or, even more confusingly, All Initial Caps), plenty can't be distinguished from the comments left by tech-savvy commenters when it comes to writing skill.
In fact, "strangers" are more likely than natives to write their comments in ways we all learned in school. In most of the threads I have studied, they make it clear who they are addressing ("Dear Facebook,") who is writing ("Thanks, Linda") and even how to understand where they are coming from geographically. They do this to the point of redundancy, sometimes entering this information into more than one comment field.
via readwriteweb.com