Cantonese "yat lau yat" (meaning "one floor one") is a shortened form of "yat lau yat fung" (meaning "one floor one phoenix").
In Cantonese, "lau" can mean apartment as well as floor, and it's the former that the phrase refers to, relating to the legal business of one single WG working out of one apartment - Having more than one WG in one apartment is illegal, since it would classed as a brothel.
"Yat lau yat" in Cantonese sounds a bit like "yat luk yat" ("1-6-1"), and hence the name of that other website! "Yat lau yat" crudely translates into English as "one floor one", which of course in English sounds a bit like "1-4-1", and hence the name of this website!
In short, saying "1-6-1" in English has no meaning... Say it in Cantonese and everyone in HK will know what you're talking about. Saying "1-4-1" in both English and Cantonese has no meaning, so don't bother!
Here are a couple of better threads on the topic:
http://forum.sex141.com/eforum/viewthread.php?tid=14901
http://forum.sex141.com/eforum/viewthread.php?tid=11458