Is it a honeypot, or is it a way to monetize piracy? Imagine a user who has a pile of music he pirated over the last decade. The labels saw no money from that.
Now that user can sign up for iTunes Match and presumably some portion of that $25 goes to the big labels. The labels see $something when they otherwise would have got $nothing, the matched files are marked with the user's name to prevent future sharing, and as it's routed through the iTunes store, the user may be more likely to buy stuff as long as they're already there.
It's neither. It's a 5-year+ plan to eradicate casual music piracy by fingerprinting (and thus poisoning for sharing) a large portion of everyone's music.
Now that user can sign up for iTunes Match and presumably some portion of that $25 goes to the big labels. The labels see $something when they otherwise would have got $nothing, the matched files are marked with the user's name to prevent future sharing, and as it's routed through the iTunes store, the user may be more likely to buy stuff as long as they're already there.