Keyboard or piano?

I have always composed on my keyboard, mainly because I don't have a piano! However, I am just about to buy my first piano and expect to compose on that. But I have just seen a video of some guy composing on his keyboard, with a piano sitting unused in the background - http://www.youtube.com/watch?v=TfqmbNvm0Q8. Why would you do this? Is it better to compose initially on a keyboard before playing it properly on a piano?

i compose on my keyboard because i dont have a piano , but i compose using a notation program not a daw , and i use a piano sound on the keyboard so basically you can say that if i have a piano ill compose on it .

Mate... it's really the same thing... keyboard, piano, guitar, flute, uilliean pipes... whatever rocks your boat. The same notes come out in all instruments, same 12 notes everyone use. It's like you ask is it better to write a book on paper or on a computer... whatever you like.

Personally, I use both. I generally create the initial idea for the composition on the piano by messing around a bit, then when i come to actually write music, i record the various insturments in using my keyboard plugged into my pc, and in doing this it often changed quite a bit from how i t was on the piano. I dont write my scores when making compositions though, i do them after, so if you preper writing by score its probably better to use just piano unless you use a pc to write in your scores and your piano isnt near it.

I use both. I much prefer to compose on a real piano. It really comes down to your own preference. They both do different things.

I use my trusty 1914 Heintzman Upright. I do better when I use an acoustic piano, but I do own multiple electric keyboards.

Why would a piano sit unused in the background of a video on youtube? Maybe it wasn't in tune

I use my trusty YAMAHA :D , since I don't have a keyboard.

But as to why people use keyboards, it's mainly probably because you can record parts into DAWs that sound so much more realistic than the click and point with mouse.