Every year we have to hear about that rubbish, so let's put it all together once and for all:
 Madrid's 600m above sea-level make the Everest look pale in comparison.
 Balls are flying so high they hardly touch the floor.
 Gravitation is so weak, players play with stones tied to their feet to stay on court.
 Due to lack of oxygen players are obligated to carry oxygen tanks onto court.
No question altitude is the major factor in Madrid.
This is why if I was in charge of the ATP, there'd be an event in La Paz with a best of 5 set finals.
These suggestions have been covered in the Reform the ATP thread, the ballkids must provide oxygen at the change of ends.
They just finished a challenger in Quito, that would be highest venue now.