The issue with only storing text is that we want to support interpolation of results, including for things like plots. If you only store the text then those results will be re-evaluated every time the help is displayed. Really, you'd want to parse everything and evaluate results immediately, then store the resulting tree.
I'd better get to work on support for tables and equations then :) I can also support things like parameter lists if there's a consensus on the best way to format them.
