This was a bit of a surprise to me. I was reading through the FAQ on Bing, and they say:
QuoteMSNBot is crawling my site, so why is it not indexing my pages?
Make sure your content is viewable by MSNBot.
Ensure there are text navigation links if main navigation is pictorial-based
Ensure there is plenty of indexable content outside of <script> </script>tags
Make sure each page has unique <title> and <meta> description tags
If possible, avoid frames and meta tag refresh
If your site uses session IDs or cookies, make sure they are not needed for crawling
Use friendly URLs whenever possible
Review our Webmaster Center blog post, I'm not ranking in Bing, what can I do?
There are many design and technical issues that can prevent MSNBot from indexing your site. If you've followed our guidelines and still don't see your site in Bing, you may want to contact a search engine optimization company. These companies typically provide tools that will help you improve your site so that we can index it. To find site optimization companies on the Web, try searching on search engine optimization company.
wow....
This makes sense, MS is the underdog at this point, they are struggling for market share. Google has been tough on SEOs over the years, they've also been tough on affiliates. In recent years its felt down-right antagonistic. Meanwhile Google has a commanding lead in searches, and PPC earnings.
MS needs to have SEOs on their side, with only 30% of the market share many people ignore Bing/Yahoo and just concentrate on Google. Being friendly to SEOs and not antagonistic can help them grow their business as the SEOs (Consultants) bring their customer's attention to Bing.