Rant: Why Are EPs So Different?

I've noticed a trend; band's first release - often an EP - is very consistently different from the sound of their first album, many times for the worse.

When I find a new band I normally don't like to start with their first album, especially if the group has been around for awhile and released several full-lengths. I like to either begin with the most current album and work back, or start from album three, after the group has discovered their comfort level with their sound.
I do this because alot of times the sounds between albums vary drastically; either the band moves towards a more commercial sound, or the opposite, where the band dislikes the way it tried to posture itself for the masses and moves off the deep end. Very few groups keep the same sound all the way through their career.
And I'm not saying that a little bit of experimentation is bad, I like bands that let their sound grow with each release. Look at Clutch, they moved from a stoner metal/rock group to a funk rock sound and now they are cemented heavily within the blues. But the steps were small from album to album, not one album they are metal, and the next one they are blues.

The three groups I want to focus on - the examples where it is the most obvious - are Fishbone, Mammal, and Mechanical Poet.

Video: Fishbone "Date Rape" (Sublime Cover)

Fishbone is a funk/ska band that was pretty big (in the ska circles) in the 80's. They started straight ska, then moved towards more of a funk sound, then got in a fight with their record company and released a couple of funk metal albums (with very little horns), then back to the funk ska. This song, "Date Rape," is from their latest studio album, Still Stuck In Your Throat, and is a Sublime cover. It's not their best song, but it is one of the best videos I found. Most of the other music videos were "very 80's" and more annoying then anything to watch.

Fishbone - "Date Rape" (Sublime Cover)