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

Rambam in the Moreh, Part 3, (will add exact source when I get a chance to look it up) posits that the days of Creation are really philosophical dimensions of Creation. (paraphrased based on memory- will hopefully give direct quotes later). 

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 occured to us as an historical event within a time-frame that can be literally referenced.