I think that point falls down about the heat for you. Most of the South American, and even some European players may play around the world now(or over the last few years), but most were born and raised in the heat & humidity. Take it from someone who has travelled a lot and now lives in a bloody hot place...It does make a diffrence.
Personally I've been here 5 years almosat and still cannot fully aclimatize to the heat. I have to have a fan or air con on most of the time and always during sport. I set my office at 20 degrees and its purely because I'm not used to the heat.
My kids on the othe hand have become almost fully aclimatised and its noticable that you youngest copes with it more easily than my eldest. I think it becomes harder to change with age.
The point about the travel is more valid but regardless of what coach they are travelling on, they still use the same decrepid roads. the air travel is obviously not an issue but I would wager that not many of the grounds will have international airports or even landing strips nearby. they will stil need to use coaches etc.
Thats just my experience & it would be intresting to hear from others like Newbury, farflung, houston and Kampala to see if it matches up....or maybe Im just odd..

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No, I take your point, I've only lived in the uk and Ireland so can't imagine the humidity in Brazil. I suppose I was thinking that highly trained athletes in top physical shape and given all the back up they need should be able to perform in any conditions and not use the heat as an excuse for poor team performance.