There remains quite a bit of controversy over the enforceablity of "Terms of Service", but many courts will enforce them, and it is not a good idea for a consumer to ignore them. Further, your assumption that the songwriter, artist, and record company "all get paid" may not be correct. Even if they get paid under Japanese legal arrangements, they may get less than they would have received had the song been purchased/downloaded from a U.S. site. I have found over the years that Japanese record labels often take a bigger "cut" than U.S. labels and, therefore, it is quite likely that a person causes economic damage to songwriters and artists by downloading the music from Japan. Indeed, downloading songs from a Japanese site might constitute copyright infringement if such downloading violates terms of sue. In addition, downloading from a Japanese site may deprive state goverments in the United States of sales taxes to which they would otherwise be entitled. Further, it is conceivable that this conduct could interfere with tax laws, regulations and foreign policies of the United States government, including, for example,laws governing when income should be recognized as having been generated from transactions that occurred in the United States. In short, there are many reasons why failure to comply with these Terms of Service should be considered a serious matter.
The first place you should look for an answer to the conflict of laws questions is the contract you enter into with Apple. In other words, the "terms of service" you are talking about may just specify what country's law applies.
If United States law applies to the violation, there is a further wrinkle: is the remedy for violation you are speaking of a contractual remedy or a remedy that sounds in tort. In laymen's terms, that means, will you be liable for having breached your agreement or for having infringed someone's copyright. If the proper remedy is a contractual one, the damages are likely to be fairly modest or limited. If the violation is viewed as a copyright infringement, the damages can be quite substantial. Indeed, if the music copyrights have been registered with the US Copyright Office, the copyright holder would be entitled to statutory damages, ranging from $750 to $30,000 per infringement- higher, if the infringement was "willful."
The courts are divided on how such a violation should be characterized- i.e., simply as a breach of contract or as an infringement of copyright. It generally depends upon whether the aspect of the license that has been violated is viewed as a central "condition" of the contract.
Obviously, without knowing precisely what the "terms of service" say, what the acts were that violated those terms, and where they were committed, it is impossible to be more precise. I hope this answer has given you some insight into how an attorney would analyze the question.
Disclaimer: This answer does not establish an attorney-client relationship or constitute legal advice. It is for general informational purposes only.