Originally Posted by ultimatemegax
Edit: After looking on Oricon and Soundscan's sites, Oricon uses 27,590 stores (a variety of electronics, convience, event, and various other stores) to calculate their estimates. Soundscan uses 4100 electronics and e-commerce stores to make their estimates. The higher amount of stores would lead one to assume Oricon to be more accurate, so that's likely why it's used.
Thanks for the clarification, no wonder Oricon is more highly regarded. I wasn't sure if it was accuracy or if SoundScan numbers were just harder to get a hold of, but Oricon is definitely more comprehensive.