It sounds like Separation of Concerns[1] applied on a larger scale. Software is easier to manage and more flexible if each piece does one thing and does it well, with as little overlap with other components as possible. This is what makes OOP a good system for designing large programs. I helps people separate out the various components so that maintenance is of many small pieces with clearly defined boundaries instead of one large piece with none.

Separating out these services into their own "apps" is like splitting up classes. It's a natural and good way to increase maintainability and flexibility.

[1] http://en.wikipedia.org/wiki/Separation_of_concerns