Only Sony/BMG is holding out now.
"Warner Music Group, a major holdout on selling music online without copy protection, caved in to the growing trend Thursday and agreed to sell its tunes on Amazon.com Inc.'s digital music store.
"Until now, Warner Music had resisted offering songs by its artists in the MP3 format, which can be copied to multiple computers and burned onto CDs without restriction and played on most PCs and digital media players, including Apple Inc.'s iPod and Microsoft Corp.'s Zune.
"The deal raises the total number of MP3s for sale through Amazon's music download store to more than 2.9 million. Warner Music's entire catalog, including work by artists Led Zeppelin, Aretha Franklin and Sean Paul, will be added to the site throughout the week. The Amazon store launched with nearly 2.3 million songs in September."
http://news.yahoo.com/s/ap/20071227/ap_on_hi_te/amazon_warner_music;_ylt=Au.FiMSJRRhT05xdshmtaP934T0D