I think you are being too literal in your interpretation of the "goals" for each month. I don't read the rules as saying that the picture has to have the word discovery in it. Rather the goal is to have a picture of the GJTB that uses the theme of "discovery". This could mean that the picture has the words discovery in it, sure. But it could also mean that the picture depicts an act of discovery, a location of discovery, etc.
Regarding your point about editing of the pictures, I agree with you 100%. Those photos do violate the rules (but many of them are fun to look at!)
BTW, we are new to geocaching and weren't around last year for the 2005 Jeep TB contest. Were there this many entries last year, because I am amazed at how many photos people have submitted!!