Maybe you might want to go back and read through your old school notes. I have never seen a claim, anywhere, that spaces don't belong after commas or periods. Look at any printed material, and you will see that spaces follow most punctuation. I was taught that one space separates elements within a sentence, and two spaces separate sentences.
In proportional font word processing, you should avoid double spaces since it can cause weird line and paragraph breaks. I'm with you on the space following commas, periods, colons, etc. and it's hard to believe someone being taught they aren't required. That's almost as bad as typing in all caps!
http://mcli.maricopa.edu/files/dvl/Word2007-Assignment-Finished.pdf