Why cant we simply type G-O-D 
You were understandably confused about g-d and G-d, Ashish, because some of our posters obviously have a love-hate relationship with the shift key of their keyboards - even when it comes to writing the name of G-d.
As for your more serious question, it's a complicated one. You might try reading this very long but interesting article in Wiki about it:
http://en.wikipedia.org/wiki/Names_of_God_in_JudaismTo state it briefly, Jews believe that the name of G-d, in any language, is too holy to speak aloud (or write down) except at the temple in Jerusalem (which doesn't presently exist), and perhaps even then only at certain times and only by certain persons.
Accordingly, "G-d" and "L-rd" are often written without the "o" even though the real name of the L-rd G-d is according to Judaism neither of those words, and even though "G-d" and "L-rd" are frequently spoken aloud by even the most devout Jews.
Confused yet? I don't blame you. So am I.
All of these beliefs, interestingly enough, correspond to an ancient Babylonian one that the name of the deity Marduk was too holy to take lightly - hence, he was more frequently referred to as Bel, "Lord".
You will often hear Jews refer to G-d using the circumlocution HaShem, "The Name".
