There were 468,000 marathon finishing times recorded in the USA in 2009; here is a breakdown of the numbers (click to expand).
You can see that the difference in average times and qualifying times is pretty consistent. The total average percent difference for men and women is only different by about .6% which is amazingly close. This means that across all age groups both men and womens' qualifying times are an average 23% faster than the national average times for all runners.
If we drill into this more and break it down by age group we can get some further info.
Let's focus on the 35-39 age group. There is a difference of 28:25 in the average times for male and female as opposed to the BQ spread of a half hour. That one minute 35 seconds represents a 5.57% difference in allowed and actual times which seems to be a sizable discrepancy. But if we then look solely at the differences between average times and BQ times we see that the difference shrinks to only 2.97%; showing that the assigned BQ times are very close to being the same percentage of the avg times for both men and women. Statistically there is very little difference between the male and female numbers and so I could probably conclude that it actually isn't easier for women to qualify.
These numbers don't necessarily tell the whole story though. For instance, the avg times include the nearly 42,000 people who finished over 6 hours. Further breakdown would be needed in order to determine what age group these runners fall in to. Obviously if a large portion of them fall into one age range this would skew the avg time much more than an age group with very few 6+ hour finishers.
Seeing the numbers it would appear that women do not have a statistical advantage over men in qualifying so there is no need to tighten the requirements on the women alone. It will be interesting to see what he BAA does to try and mitigate the rush of registrations we saw this Monday. Was it a self-perpetuating fluke fueled by unfounded rumor? Or is this indicative of the marathons future? Only time will tell but if this continues I fear it may become a harsh reality for those of us who may be good enough to qualify today to see our chances of qualifying become increasingly out of reach.