Them and their damn custom crap!
My two cents:
1) If you are an author, you have to use them to post a story. So if you can use them to post a story that you (I assume) want other people to review, then don't use the reCAPTCHA as an excuse as to why you don't leave a review.
2) Yes, they are annoying. Yes, they suck. Yes, I hate it too. But I don't have anywhere near the number of staff needed to sweep the archive daily instead of weekly for spam etc and remove it, so it stays. As Rogue pointed out, refresh is always an option (Cause sometimes it takes a couple to find a decent one) or just C&P the review.
Bottom line - the one we have is the best free option out there that has an audio option for our visually impaired users and doesn't require flash/java to use. If people want to pony up the several hundred dollars needed to get the best paid option that is a comparable in terms of stopping the spambots and has those features, please, let me know and we'll see what we can find!