I think the inteligence of the average footballer - on the pitch, not in general - has reduced massively from when I first started enjoying football. As Burn says, athleticism is paramount, although I do feel the overall technical level has risen in parallel. Players are regularly able to do things at speed that you rarely saw 15-20 years ago.
I agree entirely with the article in the sense that I think a generation of footballers have now been produced where the age old wisdom of defending hasn't been passed down to them; because of the academy systems and how they function, what they look for, what they prioritise and the coaches they employ.
The game has improved in a lot of ways but the fact that England go to the Euros with Gary Cahill and Chris Smalling as their best centrebacks is sad.