It's not the quantity, it's the quality that matters. Google has stated this publicly and while it's impressive they're indexing your site every few seconds, that might not be a good thing, or the 'right' thing for a search engine to be doing.

I could care less which search engine has the farthest reach (with few exceptions). What I (and most users I would suspect) really want is the best set of results that fulfill my query.

Except it's really hard to know the quality of the page until you actually crawl it. PageRank graphs only take you a small percentage of the way to judging quality.

If I had to guess, this is largely a scaling issue which Google has dealt with admirably. I doubt bing has anywhere near the capacity (yet) to do the level of indexing as well as google.

If it catches on I'd expect the visits to increase.