Really? I thought they are lossless apple format m4a?
Protected AAC files:
iTunes 4: About iTunes Store Song Bitrate
Purchased songs are encoded using MPEG-4 Advanced Audio Coding (AAC) format, a high-quality format that rivals CD quality.
Songs purchased and downloaded from the iTunes Store are AAC Protected files and have a bitrate of 128 kilobits per second (kbit/s).
The purchased song should sound as good as or better than a 160 kbit/s MP3 file. Because the bit rate is lower, though, the AAC file takes less disk space than the MP3 file.
ITunes Plus files:
iTunes Store: iTunes Plus Frequently Asked Questions (FAQ)
iTunes Plus is the new standard on iTunes. iTunes Plus downloads are songs and music videos available in our highest quality 256 kbps AAC audio encoding (twice the audio quality of protected music purchases), and without digital rights management (DRM). iTunes Plus music can be burned to CD as many times as you need, synced to any AAC-enabled device (such as iPod, iPhone, or Apple TV), and played on any Mac or Windows computers you own.