:::::::Camins, I think we need to be sincere in our discussion, or it would undermine the mutual trust on Wikipedia. When you give me a link like http://endic.naver.com/search.nhn?&searchOption;=all&query;=%EC%88%98%EB%8F%84%EA%B6%8C&isEngVer;=Y (note I change the interface to English so that others can read as well), it is unfair for you to select only the meaning that caters your argument. The most precise meaning for 수도권 is capital area, capital region, capital territory, etc. Metropolitan Area is also listed because it is often used to refer to a country's capital, as in the case for Seoul, London, Tokyo, but not always (NYC is a counterexample). Now, I know the problem like NYC does not exist in Korea, so this is only the minor part of our discussion. 
 :::::::The major part of whether to use subway or railway for Jeoncheol. Again, I think it is very unfair for you to abuse the term official, when what you are posting here are just sources from naver.com which certainly is not the official representative for Seoul subway or the whole wide-area railway system. naver.com is only a third-party source, just as http://www.urbanrail.net/as/kr/seoul/seoul.htm. BTW, I think you are not entitled to say Please do not mention unreliable third-party sites in this context. Third-party sources are the very citations Wikipedia need, and the wide usage of urbanrail.net on Wikipedia as a source clearly refutes your assumption that it is unreliable.  
 :::::::I do not deny that the current subway map includes both Seoul Subway lines 1-9 and other non-Seoul Subway, but this does not mean there should be a single Wikipedia page for both Seoul Subway and the Capital Area Electric Railway. The London Tube map includes both the Tube and other non-tube lines like London Overground, DLR, would you say they should all be combined as a London Metropolitan Subway or something? Note that those lines are also integrated. Seoul situation is similarly to London. Seoul Subway is the equivalent of London Underground, and in Korea, as you said, it is used for various counting purposes. Also, Seoul Subway have different operators with other lines. Seoul also have other railway lines which are not part of Seoul Subway but integrated just as London's Overground, DLR. I do not see why we should mix Seoul Subway with Sudogwon Electric Railway. There should definitely be two Wikipedia articles for the two, in particular when the Korean Wikipedia (along with Chinese and Japanese) have been maintaining two independent articles for ages.