Let's assume last.fm did indeed provide information to the RIAA. Won't we find out the truth once the RIAA starts suing people based on that information? Surely last.fm would plan for something like that instead of issuing denials.
This leads to one of two conclusions: either (1) last.fm isn't guilty, or (2) the RIAA doesn't intend to act upon the information they got. If (2), why did they request the information in the first place?
Personally, I'm inclined to believe the TechCrunch story is nothing more than linkbait, and last.fm is trying to give them as little attention as possible.
For (2), the RIAA could act upon data from last.fm without mentioning that they were using the data from last.fm
Examples: RIAA uses last.fm data to find IP addresses of people they suspect of filesharing, and then tries to find other evidence on those IP addresses breaking copyright etc. The filesharer gets busted based on the additional information and the last.fm data never gets mentioned.
For (2),
They were trying to catch the guy who leaked it from the inside… not sue everyone who listened to the new U2 album. </quote> [from the comments]
This leads to one of two conclusions: either (1) last.fm isn't guilty, or (2) the RIAA doesn't intend to act upon the information they got. If (2), why did they request the information in the first place?
Personally, I'm inclined to believe the TechCrunch story is nothing more than linkbait, and last.fm is trying to give them as little attention as possible.