Except in this case, most store duos are at pretty inconvenient places in regard to distance from living centers and in my home town, a large variety of small pharmacies with better locations closer to their customers and easier to reach beat out these guys regularly, despite not being able to compete in many pricing practices.
Truly, in my experience with Walgreens and CVS, the decision is solely one where the store attempts to grab its competitor's customers, rather than provide convenience to customers. Even when I visited Denver, Colorado, on the 16th Street Mall, a long pedestrian-only road, the only two pharmacies were on juxtaposing street corners, despite the fact that another area reached more foot-traffic, among other things.
I normally see logic in different fast-food places opening up in similar locations near interstate exits and the center of busy population centers. The issue here is that often, with CVS and Walgreens, that's not the typical case.