Hmm, I wouldn't say games are becoming too easy, but rather that they were previously too difficult. Remember, alot of older games were built around the "succeed through repetition" or "coin eating" philosophy.
Alot of games do start off rather easy, but they get harder as they go along, and in many cases you can still create your own challenge by using the game mechanics.
Look at Super Mario 3D land for example. I felt it was way too easy until I got to the second set of worlds, and boy was that difficult for me at first. Now, for me the game was very easy whenever I had a tanooki tail/suit, since the slow fall was a god-send. If I wanted to ramp up the challenge, I could play through levels with no powerups or stick to non tanooki powerups since I don't do so well otherwise. And my son-in-law who is now 8 years old finds the game difficult anyway, and he has been playing Mario games for a while now. He still has trouble with NSMB on the DS, but he isn't exactly bad at the game or anything.
Even Final Fantasy XIII-2, which I thought was in itself the easiest Final Fantasy game I have played, made it easy for me to control the difficulty curve, as did XIII (although by default it was harder I thought). Since you control your leveling to an extent, you just hold off on boosting your characters. XIII-2 was a fun and occasionally difficult game for me when I leveled sparingly. The bosses offered more challenge, and even the random encounters took a few attacks to take out. I thought it made it more fun, but if I wanted to do a quicker re-play I could just level whenever I had points and breeze through it.