Oh, and to answer the original question of why, as a webmaster, I only optimize for Google, it's because I only get traffic from Google. I've tried and tried to optimize for the other engines out there, and the traffic increase is super minimal. In fact, the traffic they send in the first place is super minimal.
Additionally, Google has Matt Cutts and an entire team devoted to interacting with the webmaster and SEO community, they have a good collection of webmaster tools, and they are very webmaster friendly. Unlike the other engines, they do give some guidance to webmasters as to what is expected of them (of course, not nearly as much as webmasters would like, but compare what Google does for us to what the other engines do!)
Its not only Google that you are doing SEO for. It is only Google that seems to be good at catching everything from your blog. I have to admit, it is easier to get indexed in Google than Bing or Yahoo.
Google also offers ( for free ) seo tools.
People optimize for Google as it has up to 70% of the market. I would rather be second result form 70% of searches then no 1 from 30%.
Hope you got my point of view.
First of all Google is the best search engine which having more regular users. It helps marketers to reach their audience via google. Most of the successful business used Google to get this position that inspires others too.