[danpalmer]

I had this same thought, but I wonder if it really matters for this use-case. The rules are actually quite simple much of the time – they're spelling and stylistic corrections.

I suspect the biggest problem with using regexes is over-suggestion, trying to correct American English spellings in a quote for example, but I suspect this is a pretty good balance of features, usability, and correctness.

One issue that comes with more complex systems like you mention is that the bugs become more complex. I'd imagine it's fairly easy for a journalist using this tool to know why an incorrect suggestion has been made, and that makes it easy for them to disregard it. While the error rate may improve with more complex analysis, those errors that do still happen are likely to be less understandable.