No, not everyone is capable of a 40+ score. (*gasp*!)
There are some skills (e.g., critical thinking, language ability, problem solving) that are extremely hard to improve.
Let's take someone who has never spoken a word of English until he was 28. Getting this person to a 40+ would probably be pretty hard (no matter the time/resources) because of the verbal section (not to mention, reading the passages on the science sections would be hard too).
Likewise, some people are just naturally more "intellectually gifted" (define this however you want - whether it be better critical thinking skills, better analysis skills, better problem-solving skills, etc.) than others. To make things easy, let's say IQ is a general measure of intellectual ability. If you take someone with a 220 IQ who is a native English speaker, s/he could probably reach a 40+ if given enough time/resources/prep. However, if you took someone with a 20 IQ, I doubt unlimited time/resources/prep would help much.