Actually inflation for the most part wouldn't matter. The 77 cents is income earned by women compared to a dollar made per male, so it's measuring a ratio, not a fixed amount which would be influenced by inflation. For that reason you can look at what the gap was in the late 60s and compare it to what it is today and not have an inflationary loss like you would with dollar amounts.
Why the gap exists, or if the causes of the gap have changed with time is another interesting discussion.
Also interesting is what constitutes "discrimination" In reality, people discriminate all the time. Hiring someone who has more skills is to discriminate on skills.
As people are beginning to see that employers are not discriminating based on gender, feminists are beginning to argue more that the discrimination against women came before they started looking for jobs. They are arguing schools are discriminating by forcing women into majors with lower paying career options for example.
I certainly agree, that people often argue the same old numbers even when they are out dated, especially when those numbers sell their case better than more current information.
(Jess - Obama used the 77 cents in at least some of speaches supporting the fair pay act, and I agree it's something that's been used for a while and is just stuck as a constant even though it really isn't a constant)