I personally prefer 77W to A380. Too many biz seats on 380 for a good service IMO. Sorry to hear ops equip change, but it's very common and certainly do not justify upgrading you to first class.
Also, Asiana also has these equip changes as well(more often than KE due to lack of avail aircrafts) so such inconvenience is not limited to Korean Air.
There are other worse things that could have happened - you should be glad that KE flew you to your destination on time on same class. I encourage you to read some of the ridiculous treatments on other airlines on flyertalk.