Yes, it's mostly an anti-trust lawsuit. From
the complaint:
COUNT I: MONOPOLIZATION -(For Violation of Section 2 of the Sherman Antitrust Act, 15 U.S.C. §2) Violations Resulting from the Unlawful Maintenance of Monopoly Power in the Portable Digital Media Player Market
COUNT II: ATTEMPTED MONOPOLIZATION - For Violation of Section 2 of the Sherman Antitrust Act, 15 U.S.C. §2) Violations Resulting from Unlawful Attempted Monopolization of the Portable Digital Media Player Market
COUNT III - (For Violation of the Cartwright Act, Cal. Bus. & Prof. Code §§16270, et seq.)
COUNT IV - (For Violation of California Unfair Competition Law, Bus. & Prof. Code §§17200, et seq.)
COUNT V - (For Violation of the Consumers Legal Remedies Act, Cal. Civil Code §§1750, et seq.)
COUNT VI - (For Common Law Monopolization Business Practices)
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The class action's complaint is that once they bought players and music from Apple, they were trapped into buying more expensive Apple players in order to retain the ability to play their music.
Their analogy was that buying digital music should've been like buying a music CD, where any CD player could be used.
The lawsuit claims that by actively working to stop any compatibility, Apple used their market position to force users to stick with Apple's higher priced playback devices.