It's really hard to say. I would like to say sometimes, letters are pretty important. If a distinguished professor wants to give you letter, then you will get much better chance. Sometimes, you do get good letters from excellent professors in your own country, but the admission committees may not know those professors well.
Similar reasons for other materials.
Also basically, I believe the educational system may be quite different. For example, in US, for undergraduate and/ or master students, it is really hard to write papers or collaborate with professors. Sometime, you may help professors to do some simulation studies, and they pay you money, and your name won't appear on the paper, but those experiences are beneficial for their applications, even though they don't have their own papers.
I hope those make sense to you.