I didn't register my sites with them either but they crawled them anyway! I guess it's a wise idea though if they haven't!
Google and yahoo are not in same algorithm so it can't be happens you are talking.after all they are also use different technique
My site is getting serps in Google but yahoo and bing are not giving any traffic to my site. It's really confusing.
I have found a lot of variation in yahoo ranking format some times keyword automatically is removed without any prior notifications from yahoo search engine.
yes day by day yahoo and bing improve their service and try to make more users but i dont think so that they can cross google