Within the, slightly mumbo jumbo, world of research into team dynamics (yes it exists, yes it is a surprisingly large field) they relate this to something calle

Within the, slightly mumbo jumbo, world of research into team dynamics (yes it exists, yes it is a surprisingly large field) they relate this to something called "information richness". i.e. Speaking to someone face to face includes visual and tonal clues to accompany the information. Digital communications can be a lot less rich (the worst being discussion forums and similar) which causes all sorts of complexity problems - a lack of engagement, misunderstandings, offence taken at wording (we all know how tough sarcasm is to convey online I am sure). Then you factor in the problems of different timezones, company and country cultures and varying tool preferences and, yes, it seems obvious that virtual teams will suffer. This paper seems pretty good from a quick read through; however I think there is a big caveat - they are studying academic research papers. Which is fine, but only one data point. A lot of effort has been put into new management techniques for remote teams and, nowadays, within a corporate project you will often find virtual teams working as efficiently as (or even better than) co-located equivalent. But you need a good team manager to pull it off.