Servos do seem quite similar to linear velocity. However, servos allow you to set limits to the force on each axis individually. For example, if you have a linear velocity acting on an object while a key is pressed and the object goes over the edge of a cliff, it won't fall until the key is no longer pressed. Servos you can have it fall right away (or not, if you don't want to).
Well, a simple motion pushes x units per logic tic, and a servo makes the object go at a velocity (units per second). You can convert like that, or just experiment to get an approximate match. I have a servo at 5.00 and a simple motion at .085 doing the same thing.
The main difficulty in using servos is that even after the actuator is deactivated the object keeps moving because it has momentum.
Edit: I found a tutorial/demo blender file that may help.
http://www.tutorialsforblender3d.com/GameDoc/Movement/Movement_Script_4.html