I think the chances of getting a GPS included in your rental without requesting it are about the same as in the US; It may happen but I wouldn't depend on it.
Getting a GPS here is probably a good idea. You can learn how to use it and preload points of interest.
The Tom Tom 920/930 and Garmin Nuvi (not sure the number) are the only ones I know of that have both Europe and North America maps preloaded. The others either charge a lot to add Europe maps or can't add them.
I leased a car on my last trip and didn't get a GPS ($100 extra). I was fine in the North but when I got to Italy, I really wished I had one. I wasted a lot of hours asking directions trying to find parking and addresses in Cities and towns.
I recently bought a Tom Tom 920 for $350 online. The price should be going down because they just introduced the 930. I like it because it has driving, bicycle and walking mode so I can carry it with me after I park the car.