The United States Registrar of Copyrights has characterized allofmp3's music as "pirated":
You've pointed to the lack of information about allofmp3.com on RIAA's website as indicating that the RIAA at least tacitly acknowledges that allofmp3 is legal:
To the contrary, the RIAA is a member of the International Intellectual Property Alliance (IIPA), a private sector coalition formed in 1984 to represent the U.S. copyright-based industries in bilateral and multilateral efforts to improve international protection of copyrighted materials. According to the IIPA website, "IIPA and its member associations track copyright legislative and enforcement developments in over 80 countries, working with U.S. government, foreign government and private sector representatives. IIPA’s goal is a legal and enforcement regime for copyright that not only deters piracy, but that also fosters technological and cultural development in these countries, and encourages local investment and employment."
IIPA representatives have
testified on a number of occasions before the U.S. House of Representatives Subcommittee on Courts, the Internet, and Intellectual Property regarding intellectual property theft in Russia. IIPA has repeatedly reported to the U.S. House Subcommittee that the Russian government should take steps to curb intellectual property piracy, which it estimates costs U.S. companies $1.7 billion annually. One of the "six critical steps" that the IIPA recommends the Russian government take is to "immediately take down websites offering infringing copyright materials, such as allofmp3.com, and criminally prosecute those responsible." Clearly, the IIPA does not believe that allofmp3 is legal.
IIPA has urged the United States to take actions to "mandate Russia compliance with international norms and obligations" regarding copyright enforcement. IIPA has urged the U.S. to: (1) Condition Russia’s entry into the World Trade Organization (WTO) on meaningful copyright law enforcement; (2) Designate Russia as a Priority Foreign Country (PFC) after the on-going out of cycle review by U.S.T.R.; and (3) Deny Russia’s eligibility for the Generalized System of Preferences (GSP) duty-free trade benefits.
Your supposition that RIAA has not taken any action against allofmp3 is incorrect. The IIPA report to Congress notes:
The emphasis is mine, but it highlights that it is much more difficult for RIAA to sue a Russia organization in Russia than it is to sue individual copyright infringers in the U.S. For that reason, the RIAA, through the IIPA, has pursued relief through diplomatic measures. While it apparently has not been very successful in those efforts to date, your argument that RIAA has somehow tacitly acknowledged that allofmp3.com is legal is flat-out wrong.