Why have periods inside quotation marks?

I was reading about Internet Explorer 7 and that they’ve turned on ClearType by default. I ran through the Windows XP ClearType tuner, and made ClearType look acceptable on this Compaq TFT8030 powered by pixelworks. Apparently it uses the rare BGR subpixel order. Then I read about using double spaces after periods (don’t), and about why periods go inside quotation marks. Apparently, the periods in typewriters could break off. Then I read Quotation Marks: Where Do the Periods and Commas Go–And Why?. There are some interesting ideas there I’ve never heard of before. Notably:

• Universal American usage always puts commas and periods inside quotation marks, regardless of logic.
• Other sentence-enders, like question marks, are based on logic: they go inside when they’re part of the quote, outside therwise.
• There is an exception for when the item is just a letter or a number, in which case it always goes outside.
• The buried treasure was marked on the map with a large “X”.
• On this scale, the highest ranking is a “1”, not a “10”.
• With parenthetical citation, the period follows the parenthesis, of course.
• This is all strictly American usage, and the British just do it logically.

I do it the British way because it’s more technically accurate, which is extremely important when dealing with the exacting nature of computers.