Is it safer to host data access in a web service rather than in a class in the current project?

We have several projects in which we put all the data access into a separate web service project, and the parent project will call the web service for all related data. The web service will only accept connections from the web project server. My guess is that the web service will be less susceptible to intrusion in this way. I am not sure if this is correct.

Is it safer than just sharing data in a class or dll in a parent project?

Note
The developers above me made this decision.