I'd be surprised if Apple did any checks on the bitrates they receive, other than possibly making sure they're at least 128. As someone else said, the labels encode the music and send it to Apple, so there's definitely room for variability. I'll bet that the songs in question were encoded at the higher rate, whether intentionally or not, and Apple simply accepted them.
There's a lot more info on the whole process
on this page. Specifically, it says:
- It's up to the partner/label to submit all the metadata (artist name, release date, song tiles, etc.), do the audio encoding, and upload the materials.
- You have to use their special Music Store Encoder tool for Mac OS X which will be released in 90 days or so.
I always thought it seemed a bit surprising that Apple has the labels do the encoding. Maybe the labels demanded that just because they wanted more control, who knows? The problem with the current situation is that most of the labels probably encoded once, sent the 128 kbps songs to Apple, and that's it. That means it would be a
massive undertaking to move the whole store to 256 or whatever. Everyone would have to re-encode, and there may be cases of songs where it's difficult to get the label to do it again. It would certainly be a long a drawn out process, even assuming they could convince the labels to do it again.
If Apple retained a full quality copy of each song as part of the package sent by the label, then they could make this kind of switch at any time. Just throw a few dozen machines at the task and let them crunch for a few days/weeks or whatever it takes. Instead, it's pretty clear that they expect to offer 128 kbps as their standard for many years to come.
Kinda makes you wonder, when the first competitor comes out with higher quality downloads, will that be the turning point when iTMS starts to lose major market share?
Then again, maybe the labels are demanding no more than 128 kbps quality because they fear that higher quality would attract more piracy. Gotta love an industry that fears its customers!