They both came out in NA the 11th January 2005, i havent finished Resident Evil 4 yet but i love Mercenaries: Playground of Destruction, in my opinion the best sandbox of all times after Grand Theft Auto: San Andreas.
Just got the GC version of RE4 for christmas. SOO MUCH FUN!!! I think we might also celebrate some other game's 10th birthday as well. Conker: L&R, Castlevania: Dawn of Sorrow, as well as Shadow of the Colossus. 2005 was a great year for gaming. But I dunno about 2007...
Mercenaries was awesome. It probably still holds up nicely, specially on the Xbox with 480p and 16:9 support. And yes, it's another franchise killed by EA.
RE4 is a double edged sword for me, It was fun as all hell at the time....but it led to RE going in a completley different direction Merceneries was a pretty fun game for its time too, the fact you could almost destroy anything was so cool