Sure musicians are salesmen, but not necessarily desparate ones. They're basically running a business where they have to sell their product. This applies at all levels, even if you're a no-name local act trying to get people out to your gigs. I'm sure most of us aren't seldom influenced by this and view it as them merely going through the necessary motions, but 't personally believe generating that kind of hype is totally inconsequential and pointless. I certainly made a few blind purchases this way in my early teens based on a band's praise of their newest work. Call me gullible, but I doubt I'm the only one.
Just the same, it's probably worth considering that the band often perceives their work differently than the consumer. The consumers only get the final product to base their opinions on. On the other hand, the band is there from the earliest writing stages all the way through the recording and pressing, and I'm sure many of them factor in those experiences when formulating an overall opinion of the music and the record. They could record songs unanimously viewed as downright horrid by the fans, and the band themselves may ultimately share those feelings. But perhaps they also had a really pleasant studio experience or the band members were better able than ever to collaberate on the writing or something like that. Even if they feel, deep down, they like some of their older material better, they still might feel fairly accomplished and successful because of factors like this. Sure it's biased, but everyone has biases.