CBS-owned social Internet radio service Last.fm once had content from all four major labels, but now Warner Music Group, which had been licensing to Last.fm on a month-to-month basis, has pulled its catalog from the service.

As first noticed by Silicon Alley Insider on Friday, it appears the main impetus for WMG's withdrawal from Last.fm's streams is, of course, money. The major label simply wanted more money from CBS, and was reportedly "disappointed" that a Last.fm premium subscription service was not opened as was anticipated.

The loss of one of the "big four" labels -- the other three being Sony BMG, Universal Music Group, and EMI -- could definitely cripple the service, as other music ventures have struggled against an inability to carry all the majors. Furthermore, WMG is offering its catalog to quasi-competitors (offering similar, but not identical services) Imeem and the forthcoming MySpace Music.

However, Last.fm today flouted the loss of WMG in its free streaming service by announcing its second-ever exclusive album pre-release there. Today, the new Sigur Rós album Með suð í eyrum við spilum endalaust, is available to be freely streamed in its entirety on the site, two weeks before its official release.

It's deals such as this one, which involve the capability for artists to be compensated directly, bypassing the traditional royalties route, that may be contributing to Warner Music's current objections. Last.fm has pre-released an album only once before, with legendary trip-hop band Portishead's newest album in April. That particular album was reportedly streamed over 300,000 times.