It's not same...
Take look at ASSCI table
http://www.asciitable.com/index/asciifull.gif
"G" and "g" are just constant. You also could write 71 instead of "G", 103 instead "g".
IF command[0] = "G" AND command[1] = "C" THEN
is same as
IF command[0] = 71 AND command[1] = 67 THEN

For parsing string commands I use this:
http://www.picbasic.co.uk/forum/show...009#post117009
Scroll down code to CommandParser: label.
You can easily convert upper case to lower and lower to upper as in this sample
http://melabs.com/samples/PBP-mixed/serin.htm