The real question is: is it legitimate to go back and change your rating? That's why I have always been a proponent of a "cooling" period where new releases are not rateable. Text reviews should always be welcome, but quantitative ratings are, as the premise of your post, skewed by the (won't use the 'f' word that ends with 'boy') people who are predisposed to grab their favorite band's new album the minute its released.
Everybody's taste changes and like it or not, albums sometimes don't stand the test of time. There was a time when there was an extremely limited number of progmetal bands. I regarded Dream Theater very highly for the first 2 albums. Now that i know what was really out there, and what has been subsequently created that is light years better than DT, they bore me, and in some cases, completely annoy.
The Wall, used to seem so profound. In its case, its not just other music, but reading and life experience that really exposes
The Wall as a 90 minute transferal whine by a self-absorbed masochist.
So I guess, yes, we (meaning everybody else

) are too generous. But really, the ratings say more about the rater than the album. That's why its a good idea to look at member profiles and get an idea of what they like and how the give ratings to really determine if what you are seeing is indicative of quality, or just personal taste.