Back in the '60s and early '70s, musicians were expected to release albums at a blistering pace. Consider The Beatles, who released at least 12 or 13 albums (being conservative by not counting repackagings and compilations, and depending on which ones you count as "real" albums) in a little over seven years between 1963 and 1970, plus various singles (like "Penny Lane"/"Strawberry Fields Forever") that didn't appear on LP before they broke up.
CCR were more prolific, putting out seven albums in just over four years—three of those in 1969 alone. Led Zeppelin's first four LPs emerged between 1969 and 1971. And so on. Even R.E.M. reliably put out an album every year through most of the '80s.
Contrast that with someone more contemporary, such as our hometown girl Sarah McLachlan. Her recording career spans close to 20 years now, since her debut Touch in 1988. In that time, excluding remixes, re-releases, compilations, live albums, and other side projects, she has put out five (yes, five) complete studio albums of new material. Six if you include last year's Christmas disc (I don't usually count "very special" holiday releases of traditional music as real albums, but you can if you want). That's something between 55 and 70 new album tracks (again, depending on how you count) over her entire career, or an average of three or four new songs per year.
Fall Out Boy are still in the initial bloom of their career (work with me here, I'm sure many people think they're totally passé by now, but I need to talk about bands that are more than a year or two old), and they've put out four albums in almost six years. That's pretty quick these days, but in their heyday Creedence would have lapped those emo cuties several times by now.
Peter Gabriel exemplifies the trend. After he left Genesis, he released solo studio albums in 1977, 1978, 1980, and 1982, not a bad clip (especially considering how groundbreaking some of them were). Then came So in 1986, which seemed a long wait, but Us took until 1992. Up didn't show up for ten years, in 2002. And his fans are still waiting for the next one.
I understand that the industry has changed. Fans don't expect a new album every few months anymore, singles have come back thanks to iTunes and other download services, tours are more extensive, there are videos and DVDs and other projects on the go. Digital studio technology means artists and producers can obsess about and try to perfect tiny details of tracks for months or years on end (hello, Stevie Wonder?). Bands back in the '60s often burned out from the relentless pace their customers and managers and record companies demanded (the Beatles included—by the time George Harrison, the youngest of the group, was recording his parts for Abbey Road, he was only 26, but he looked a lot older).
But you know, if I liked a particular artist, I'd feel a bit cheated if they couldn't put together more than three or four decent new tunes a year. These people are musicians, this is their job. In the mid-'60s, Bob Dylan was probably putting down three or four great new songs before lunch some days.