Plus there's the fact that the song was composed by Hirokazu Tanaka. This is huge since Tanaka hasn't composed anything for over a decade. Actually I think the last game he composed music for was Mother 2 back in 94.
Also this quote could prove important.
Quote
He wasn’t included on the list of musicians until now, but he secretly joined the fray!
This makes me wonder if any other composers have joined. Since this game is looking to become one big tribute to videogame history, I'm sure there's lots of composers that want to be a part of it. So I'd imagine over since the site first opened last May there's been several other videogame musicians who have come to Sakurai wanting to be part of the action. Since music is the easiest part of the game to add, I'd imagine that they're still might have some new musicians still composing music for this game even as we speak.
Plus since the CD's are a collectable like trophies and stickers, that means there's going to be a lot of songs. Since Melee had over 290 trophies to collect, Brawl could have around that many CD's to collect. That's right, we could be looking at around 300 songs being in this game, and with all the musicians they have, it's very possible.