Soton are not lazy (then again i would say that). Contrary to popular belief they do interview a fair few gappers and people they want to know more about for bm5 so they do look at applications carefully. Their reasoning behind not interviewing the majority of the candidates is that they believe an interview creates a false atmosphere for them and doesn't really tell them much. They also say that candidates tend to overprepare for interviews and go on all of these courses so you dont know if the candidate is being true or not.
In saying that one could argue that people lie on PSs and referees make up stuff giving a false impression. In a way i think admissions tutors need to watch candidates over a period of time but this would be virtually impossible