We know that Wonder Woman and Steve Trevor met decades ago and that he dies. Yet in the new 52 justice league, he is alive and is the contact between the justice league and ARGUS. How is he alive? Did his origin get revamped in the new 52?
tl;dr - it's different now, for the current iteration of "now"
As the company's continuity was revamped in the various Crises (they are very much a story in themselves), the characters' histories are revamped to varying degrees, and in some cases, like the original Justice Society of America, are declared to have never existed at all.
In her original Golden Age version, Wonder Woman first appeared in WWII, after Steve Trevor crashed on Paradise Island and asked for help. After Crisis on Infinite Earths, Diana only makes her first appearance in Man's World in the present. Later, they attempted to explain the WWII stories by claiming that it was Diana's mother, Hippolyta, who had those adventures. Her current origin is quite different from her original one.
The version used for the movie was mostly the golden age story, changed to take place in World War One, with a few bits of the current "literal daughter of the gods" story.
There will almost certainly be more changes, large and small, as each new creative team decides to either fold back in facets o past iterations, and eliminate recent changes with which they disagree.
The explanation can be applied to just about every DC character, with only the details of that character changing.
To be a bit more specific:
Prior to CRISIS ON INFINITE EARTHS (DC's first "reboot" event), We'd seen the adventures of the WWII-era Wonder Woman (from Earth-2), and the present day Wonder Woman (from Earth-1). As with Superman and Batman, both of whom continued to appear throughout the 50s (Flash, Green Lantern, Atom, and most other weren't seen between the early 1950's and the late 1950's, when the "Earth-1" versions started appearing), the dividing line between the Earth-2 and Earth-1 adventures is somewhat arbitrary (pegged around WONDER WOMAN 98, after the fact).
In these, Steve Trevor is roughly the same age as Wonder Woman (and, in fact, is her romantic interest). Steve was killed off at some point in the late 60s, brought back in the mid 70s, and killed again in the late 70s/early 80s, and then sort of brought back yet again.
Following CRISIS, in 1986, Wonder Woman was rebooted, with a (slightly altered) origin story. Here, Steve was probably in his late 40s/early 50s; while a romantic relationship wasn't necessarily out of the question, it almost certainly wasn't the intention of George Perez (who authored the reboot). This version of Steve married Etta Candy.
Following the FLASHPOINT event (which ushered in the New 52 version of DC reality), Steve is again about the same age as Diana, and is again a potential love interest (especially now that we've switched to a Superman whose married to Lois Lane again [don't ask]).