... as in, most often-cited papers are older (taking some time to amass the citations), and effective collaboration tools only became available much later? Als

... as in, most often-cited papers are older (taking some time to amass the citations), and effective collaboration tools only became available much later? Also, the progress that has been made on remote collaboration (say, Skype and DVCSs versus telephone and CVS) is significant. I won't say that there is no advantage to meeting in person, regularly, but the alternative "Researchers keep high-impact work within their own lab" does sound very credible.