[ayumisrael]

In Japan, there isn't any reason to pass to billboard.
The contrary, 99% of the people in Japan trust oricon and it has the highest reputation among those sites.
Oricon is also known as the most accurate since it counts most stores in Japan.
The only thing oricon doesn't do is counting digital sales, but then I'm not sure if the billboard is really accurate too (since even RIAJ or companies and recochoku would be more reliable for how a song did digitally). That's why I think the Japanese won't shift into Billboard, for them (and for me) oricon is a way better indicator and more accurate. For digital sales, recochoku and RIAJ are the best methods I would say. That's why the combo of oricon, RIAJ and recochoku own billboard each. =P
Therefore they see no reason to shift into billboard, and imo they are right.
The popularity giver indicator probably will always be oricon (until physical sales are dead for good anyway) and recochoku and RIAJ since they are the most accurate and they count most/all of the things. It's just that each one does something different.
Oricon - physical sales
recochoku - overall digital songs and PVs ranking according to digital sales from most websites.
RIAJ - Certificating a CD and a song if it passed a mark (like gold, platinum, million).