Also, absolute limitations on page count is really common in CS, and the page counts tend to be pretty low. In other areas, journals might allow for more citations or citations might not count toward page count.
Also, arxiv is physics-biased.
Have there been any significant CS papers published in the last ~5 years that aren't on Arxiv?
The last thing I remember not being there was a set of papers on IBM Watson that were published in an IBM Systems Engineering Journal.
I have a feeling that some papers out of Microsoft tend not to end up there too, but I can't think of a specific example.
Even if not, there might be insignificant CS papers not indexed by Arxiv which cite significant papers which are indexed ;) This makes the citation counts comparatively lower if most insignificant physics papers are in Arxiv.
That said, it doesn't surprise me much that worldwide there are still more people working in physics, biology or mathematics than in CS.
I found 38k citations for The Nature of Statistical Learning Theory: https://scholar.google.com/scholar?cluster=86085598803682809...
And 25k for Statistical Learning Theory: https://scholar.google.com/scholar?cluster=86748554971781655...
My initial estimation of 10k was from a CiteSeer list that I didn't realize was limited to only documents in the CiteSeer database: http://citeseer.ist.psu.edu/stats/articles
PS. I'm not sure which paper in the arXiv has the greatest number of citations. I don't think either of these papers are there.