Counting unique landing pages in Google Analytics: social vs organic channels

[mcglynn]

Remember the technique Rand posted for counting the unique indexed landing pages on a site?

http://moz.com/blog/indexation-for-seo-real-numbers-in-5-easy-steps

I'm using Google Analytics to compare this result for the "social" channel vs. the "organic search" channel. The idea is to see whether social or search delivers people to more unique landing pages.

I would expect organic search to yield a significantly higher count, due to long tail searches for relatively obscure terms. We have an archive of over 500k pages that Google could be indexing, even if only a fraction of a percent of those might be getting social mentions. But that's not what the numbers show -- I'm seeing roughly 10% higher numbers for the Social channel than for Organic Search. Again, I'm counting unique landing pages here, not the total pageviews or visits.

If anyone else here is monitoring these metrics, please chime in with your results. What's the baseline expectation for a large website with hundreds of thousands of pages of issue-centric user-generated content? Should search traffic provide 2x more landing page exposures than social? 5x? 10x? or 0.9x, as in my case?

In short, I believe these numbers are pointing to an indexing/ranking problem following a recent site redesign.