In the wake of competition from Amazon.com and WalMart, Apple changed its tune on pricing for iTunes Plus music. iTunes Plus offered DRM-free music and higher quality audio files for $1.29 a song versus the $.99 price for those encumbered with copy protection. Now Apple is offering the Plus catalog (which now includes more Indie music) for $.99. At the moment, the only DRM-free music available on iTunes beyond the Indie selections are from the EMI label.
No word yet on how this affects the upgrade process that was put in place for those wanting to upgrade to the new format.