At user group meetings you get the Real Story, you talk to your peers. Whereas at the vendor's own annual event, you endure hours of sales pitches, and ecstatic announcements of new bells and whistles to come in the next release. Of course few people really care that much about the next release; they care about getting value from the release they currently use, typically some version well behind the latest.
I think for tech flacks, user groups are indispensable. This is the ultimate audience for your press releases. This is how you learn about your customer's customer.