Why cabbrev rather than cmap?

[Suresh Govindachar]

In another thread, Yakov Lerner wrote:

> 4) You can use tip http://www.vim.org/tips/tip.php?tip_id=1285
> to remap :w to :up :
> 
> cabbrev w <c-R>=(getcmdtype()==':' && getcmdpos()==1 ? 'up' : 'w')<cr>

Why cabbrev rather than cmap?

--Suresh