Why is “I” capilalized but “me” lower-case?
It could be (I did a very quick search on the subject and didn’t find a source - so take this with some reservations) that the usage of a capitalized “I” as opposed to a non-capitalized “me” or non-capitalized “a” is that “I” was regularly at the beginning of sentences and consistently used to represent an individual’s name.
Of course, the same argument can be made for “he”, “she”, “they” and “we” which are not capitalized.
It could also be that some of the earliest usages in English of printed matter were royal decrees, and in that case all references to the royal personages were capitalized.
Also since the lower case “i” is such a pain for printers setting type by hand to set, they could have opted for the larger and more easily grabbed letter.
TV
This similar question contains a link which may be helpful: http://boards.straightdope.com/sdmb/showthread.php?threadid=64484