I haven't bought music through iTunes yet, so I'm hardly an expert, but it seems to me that if I were to PURCHASE music through a DOWNLOAD service, I would want to "download new purchases". It seems, then, that this would be the normal and expected setting - unless perhaps one expects to purchase on cell data service and then download later on wifi? in which case it would seem the better solution would be an option in the service to only download big files while connected on wifi, but I know Apple doesn't seem to care about little things like how much you spend (after all, you bought an Apple product, you want coolness!)
Well, there are two things.
First, there's a global "allow downloads over 3G" flag that's unset by default because well, you may not want to use your data connection.
Second, there's a "download purchases" flag that's dependent on iCloud.
The first controls whether or not you want to use your data connection for immediate download. So if you buy an app/book/tv show/movie/song, and you're on 3G, then it will queue it up for download later. If it's set, it will immediately download it.
The second is when you buy same SOMEWHERE ELSE. So if you use iTunes on your PC and buy an album, then all devices with the flag set (it's unset by default) will also automatically download the album and you'll have it at the ready. So you can buy a song/album/tv show/movie/book on your PC, take your device and it'll be there if the flag is set (and if it can download it - wifi or if enabled, 3G. After all, if you disallow 3G downloads, it would be a bug to download over 3G).
What happened here is Apple marked it as "purchased" and people who had the auto-download flag set started automatically downloading the album (over WiFi or if configured, 3G). And then complained because it worked as advertised.
Apple couldn't push it to you or force you to download it. They just marked it as if you bought it already. And that was something all download services have - they could add/remove stuff from your purchased list.
The only way Apple "pushed" it is if you had auto-download enabled in which case it worked as advertised - you "bought" the album "somewhere else" and it dutifully saw that it needs to get it.
The flag is off by default because you could easily find a smaller device filled full of purchases of anything.