It appears, however, this is not a result of cloud censorship on Google's part. It's not because Google is trying to get away from what Steve Jobs once famously said, that if you want porn, go to Android. Instead, it seems like a bug.
There's a reason to believe that: Some users are experiencing exactly the opposite, seeing their clean versions of songs replaced with explicit versions. To be clear, though, it's something that Google isn't alone in seeing with their scan-and-match feature. Apple saw the exact same problem with iTunes Match soon after it debuted.
Scan-and-match technology works by scanning a user's library of music and comparing it against the provider's database of music. If the song in the service's database has a higher bitrate than the end user's song, in general, the user gets a bonus.
Google's service is free, as long as an end user's library consists of less than 20,000 tracks. Amazon Cloud Player subscribers have to pay $24.99 annually once they pass 250 tracks, although they then have the ability to store a nice 250,000 songs in the cloud.
Apple's iTunes Match is priced the same as Amazon.com's service, but limits you to 25,000 tracks. So Google's service is a bargain, except when it comes to having your explicit lyrics replaced with clean ones.
We expect this is just a bug and will be ironed out, soon.