I think that it's also to do with the fact that players on a season-long loan can't be recalled to their club, so doing it this way keeps all options open.
If anyone uses Google Calendar, here's an iCal file for one on there:
http://www.google.com/calendar/ical/0o5n7ka0e8ft57b19aviuc40jo%40group.calendar.google.com/public/basic.ics