It is really sweet when people use a diminuitive though... Seems so to me, anyway!
Isn't that a sign that you are good friends, or the person likes you?
Or could it be construed as being rude or overly familiar?
English, of course - has a fair number of nicknames too. I have noticed that the way that the nicknames are used vary quite a bit between the UK and US, with Americans using the nicknames a lot more, including kids nicknames for adults, i.e Johnny, Jamie etc
And president "Bill". (real name, William). Here is an explanation for anyone interested
http://www.cc.kyoto-su.ac.jp/~trobb/nicklist.html