Kevin does a nice job of laying out some of the competing objectives for the Olympic Marathon Trials. As mentioned before, contrary to the track and field trials that have fairly set logistical limits on how many can be in the field, in practical terms adding people to the marathon trials (up to a point) does not negatively impact the event.
So to sum up as I see it, the Trials essentially has these objectives:
1) To select the best Olympic team possible in the fairest way possible
2) Act as a marketing tool for the sport attracting attention to our best distance runners
3) Act as a development tool, giving our 2nd tier runners both something significant to shoot for (keeping them in the sport), providing a clear measuring stick aginst top tier runners, and providing the chance for a "diamond in the rough" to perhaps surprise.
How you weight each of the objectives defines how many people you let in and how you run the event. The women's trials put a different emphasis on objectives 2 and 3 then the Men's and hence you get different standards.
From a marketing perspective, perhaps a good comparison could be made to the NCAA Basketball Tourney. If all it was designed to do was select the best basketball team in Div. 1, you would not need 64 teams. Yet the marketing (and revenue) advantages are so significant for keeping all those extra teams in there you will never see the field size reduced.
The trials are different because there is not nearly the same amount of money involved but the principals are the same. In the interview with Latimer, he obviously discounts the value of the "slower" (2:19 - 2:22 runners) bring from a marketing perspective (home town paper, friends, etc) and dismisses the 3rd objective (Kevin's point).
I would argue this is the wrong approach, I think that by not having a B standard not only are you losing out on the positive marketing contribution those runners make to the race, you are also alienating a good number of running’s most loyal and best "customers" [which includes not only those who make the time but those who think they can]. If running is to stay truly viable as a sport it must start doing a better job of thinking of itself as a product. Good products do not piss off their best customers, especially ones that are young and have a lifetime of potential involvement in the sport.
That does not mean let everyone in, as that has a lot of negative consequences (example a see how valued all of those "World Age Group Championships" are in Triathlons where all you have to do is pay your entry fee to get in).
That's why I would suggest a work backwards approach - like the track trials - find a largest field size that best balances the exclusivity of the event, financial constraints, and race logistics and figure out a standard that will get you that field size (or just use a provisional standard). This field size would be part of the package that each city uses in their bid.