I think this may relate to the fact that blow can be an offensive word. I asked them on twitter why, if it scans my tweets, texts, etc why it doesn't know my favorite cuss words. Their answer was that it won't pick up offensive words from scanning, but they will be added when you type them in.
I've been using SwiftKey for a couple days now and so far I really like it compared to the stock one. Makes my typing easier especially if I need to repeat myself lol.