Exactly. If it's just a question of tactics, then how come Ancelotti and Mourinho can't do it with an English club but can in every other country? How come Roberto Di Matteo and Rafa Benitez can win it with teams that are clearly not the most talented in the competition?
It's a cup competition, so there's always an element of luck involved, especially with similarly matched sides. But in general, the countries with the better teams do better on average. The reason why English clubs haven't done well in the past few years is because they haven't had great teams. Between 2005 and 2009, we had 6 out of the 10 finalists. Since then, we've had just one finalist, because we haven't had teams that are as good as Barca, Real, Bayern, etc. Since then, Chelsea suffered a slump in quality (although ironically won the CL with a far worse team than their best), Arsenal sold their best players every season for years, and are only now getting back to where they were, Liverpool have completely dropped off the map as a Premier League force, and the rags have sold world class players, had world class players retire, and have failed to replace them.
We've struggled to get to grips with the competition for a number of reasons. We're quite unique in being one of the only teams in history to be a massive scalp before we've even played a game in the competition. We've also been incredibly unlucky with draws (well not unlucky, it's designed that way), going up against the best Bayern team ever, the best Dortmund team for decades, the best Barcelona team ever... We've also failed to be organised enough defensively in the league, never mind the CL, so it's not a massive surprise to see that against better teams in a knock out competition, that becomes a problem. Hopefully we've addressed that somewhat this season.