Can I be the person to say neither?
I mean, to an extent both things are true, as people have said. We experienced players have skill and familiarity at our backs, which is a luxury not everyone has, so games designed for a larger set of people, and games designed to be able to draw in more people, are naturally easier. Similarly, design has gotten better in terms of GUI, graphics, and controls. Actually being able to execute actions intuitively, and understand what is going on, these things make it easier.
But more than that, games have a different focus now, and the challenge is often in a different place. Call of Duty isn't an easier game than Contra - it is completely different. This can be seen in parts of the campaign and things like that, but is most obvious in that the main element of CoD now is the multiplayer aspect - the challenge is not in finding the exact moves you need to beat the game, but in being able to outwit and outperform other players.