In relation to the Wikipedia information on "students required to be Christian in order to be admitted to Yonsei prior to 2009", I feel that I should clarify this fact. The information on Wikipedia is not correct. In order to be admitted to Yonsei, religion was not considered.
You should edit it then (it's wikipedia, you can do that). It kind of makes Yonsei seem discriminatory. This would be unfair if this information is untrue.
What's the reason for SNU being top then? In Japan, for example, Keio is the oldest in Japan and actually for a very long time was the most prestigious. This dominanec began to waver when the government started up Todai. Although Keio was originally at the top, the government did not fully give Keio its support. The government discriminated applicants based on the school they went to and gave heavy preference towards the Imperial universities, especially Todai. Obviously within a couple decades, the vast majority of top positions in Japan went to Todai students for this reason. So even though the top students may have went to Keio early on, they couldn't get the top positions. Essentially, this lead to Todai graduates dominating the elite of Japan. The top students, the smartest of the smart in Japan, don't take long to figure this out. Soon the top students began to heavily favour Todai too. They began applying to Todai, and now the top talent are all at Todai. With the top students now fully choosing Todai, to this day Todai has an iron grip on Japan. This is true even if there is no longer unwritten/implicit rules to hire mainly Todai students. Today, even with no official preference by the government, the position that Todai has in Japanese society is so dominant that all the talent go there now anyway.
Anyway, that is how a Japanese student explained Todai's present dominance to me.
Why then is SNU Korea's top school? How did Yonsei manage to lose out to a school that has strong Japanese roots? Especially considering that Yonsei had the heavy advantage of being Korea's oldest school + being homegrown?