Simply because I only really use the email function on my phone to receive and reply to. I very rarely need an address on it, I wait and use a computer if I need to send something a bit longer. I do use the syncing feature though on Google to store all my phone numbers so that I have a backup if the phone was lost. Simply choose to store the number as a google number instead of on the sim card.it isnt actually. You still need a 'server' of some sort to sync with. You cant do it direct.
out of interest why wouldnt you want your contacts in sync across all your devices?