You have two very different questions here:
- how the international applicants are being treated, and
- how are math courses being evaluated.
The site would have been better off if you split them, as they are conceptually unrelated to one another. Ah well.
JeffE gave a good answer regarding the former question. His answer seems generalizable, as I've heard of other departments doing similar things. The admissions committees usually try to identify the countrymate among the faculty of their university and ask them whether the school the applicant is coming from is a worthy one. It is more difficult to do with applicants from Kenya or Morocco than those from Australia -- most academics will know about the top AU schools (and if they don't, I just gave them the link :) ).
For your latter question, there is no good answer as there are 4000 colleges * 5-50 math instructors in each. Oversimplified hand-holding you described is typical of the intro classes where the students will bitch about the letter $\theta$ and the sign $\forall$ as they have never seen it before. This creates huge impediments to instructors in trying to challenge the more inspiring and better prepared students who have to be held back at the level of the rest of the crowd.
I had a British prof in my Stat program, and he said that the British exams are usually written so that 70% completion gives you an A. I.e., the instructor reasonably expects that the top students will get 70 out of 100 on this exam. His exams were like that. As the system down under is built after the British system, you probably have the same approach.
The silly American "grading curve" system is 90-100% for "A", the top grade; 80-90% for "B", the second best grade; 70-80% for "C", which few students want to get; 60-70% for "D", which is a very low pass, and often requires retaking the course. Students want higher grades, and do not hesitate to give lower evaluations to instructors who grade less generously, so the professors, especially whose main responsibility is teaching (vs. research on the tenure track), have the incentives to make the exams simple so that the students are happy. The system produces a lot of students with nominal "A"s who know little to nothing. Only the top 20 or so universities (arguably stronger than the Australian G8 schools) have stronger incentives to maintain the university reputation, and tell their profs to make the exams real. I would expect that the stronger campuses of the Univ of California system (Berkeley, UCLA, UCSD) would know better than just hand everybody an "A".
As an artifact of the grading curve, the instructors have to populate their exams with 70% of very simple problems to let the bottom students accumulate enough credit for their "C"s, and can basically afford only one or two problems on a typical 90-120 minutes test to distinguish between the top "A" students and solid but not the top "B" students. This all is a matter of habit and tradition. Some instructors try to override it by making the total sum of scores in the course to be 431 or some prime number like that, so that there will be an extra step for the students to convert their 301 score to the familiar 100% range -- and most will fail without a calculator, and won't be able to tell whether getting three extra points they can squeeze for a homework would change their grade to pass from 69.93% to 70.05% into the next letter category. Professors coming from other countries may sometimes bring their own evaluation ideas (as my British prof did), and those interested in teaching and learning devise their own systems -- I described mine here.
Best luck with your applications, rest assured that you won't have any issues with the US schools just because you say it "todie" instead of "today" :).