Stepper vs Servo

Greetings!
I am new here to the mailing list. I have a couple of questions. First some
background. I am interested in constructing a light weight CNC machine
capable of cutting out RC airplane parts from balsa, bass and aircraft ply.
Also intend to use it to mill PCB boards. So essentially some engraving and
light cutting. From where I work I have access to some "surplus" parts from
where I work. The parts include THK rails (20"), Gurley Linear encoders
(2000 counts/cm), misc linear guides, e-chain, stepper motors, and some
fractional HP servo motors (36V). I am an electrical engineer writing
firmware & designing boards for XYZ cartesian liquid handling instruments.
We use servos for all our motion control needs. So when I decided to start
project I started research what was out there. I since discovered that most
of the "do it yourself" CNC people uses stepper motors! Much to my surprise.
So here is the questions:

1. why does everyone use steppers?
2. Isn't closed loop system required to have good control of the tool?

It appears that most of the software that is within reach supports stepper
motors (step and direction) is the reason for steppers?

Thanks for any input on this subject.

Joe