What I have noticed is that the talent is very equal in the world of the football and these tournaments are very different then club football. First of all, youth is very important. There are some players (ie, Zidane) who prove an exception but for the most part, the older players are not fast enough, do not have enough stamina or are able to work hard enough throughout the entire 90 minutes to defeat the other squad. Of course any side needs some veteran leadership but you can't make up a team these days of older, slower, not as hard working players and expect them to be able to play at a top level every 4 days. In the past, it was possible for the big squads to get by with only their skill but I think there is not that great of a skill gap between any two given teams.
If you look at who has been successful in this tournament, it has been the teams that have been able to run all day, pressured the oposition in their attacking half rather then waiting for them to cross the center line and have been willing to work their asses off for the entire 90 minutes. This is a big paradigm shift in world football and the last World Cup and this Euro are very much proof of that.