Bing Bots are slow

[Paul]

The rate of indexation changes from one search engine to another. Bing has inferior crawlers to Google's and uses a completely different algorithm for parsing and indexing content. The same number is usually never indexed from the same site from one search engine to another. This is why keyword position differs from Google to Bing and beyond

I agree with you PK. I have a little question regarding sites which has more indexed pages in Bing than in Google. Do you have any idea how these things happen?

Genarally it is not seen that someone has more indexed pages in bing than google. It can only happen when someone's site every feature totally comply with bing algorithm.