Two is an older convention, based on typewriters, and the letter sizes. Where letters like M and I took up different space, and the double space after the fullstop allowed for a more even typing presentation, and clear distinction between sentences. It is probably more uptodate, with the new fonts to only do one space. But old habits die hard...
:yeahthat: The PA to my Director in my old job still does the double spaces, but she had been around for a while