Answer to the tack-on question:
This answer may seem controversial to some, but I'll post it anyway:

Rambam in the [Moreh, Part 2, Chapter 30][1] **possibly implies** that the days of Creation are not meant to be taken as literal units of time, rather they are really philosophical dimensions of Creation.

If that is the case, we can extrapolate that our six days of action and the seventh day being Shabbat, are only a small memorial of what actual Creation was (and is) since the actual Six "days" of Creation cannot be literally referenced using a time-frame.

However, leaving Egypt can be explained as "zecher", an actual memory, because it occurred to us as an historical event within a time-frame that can be literally referenced.


  [1]: http://hebrewbooks.org/pdfpager.aspx?req=14118&st=&pgnum=384&hilite=