And there are great products out there to meet that "need". Cheap ones too.
Separately, it frightens me to know that there are people on the road who can't even find their way home without voice prompts. Actually, thats terrifying. I'm supposed to teach my kids to drive in a few years, and every day I worry about that more and more, as I have no choice but to subject my loved ones to the (lack of) driving skills of the general population.
What are you even talking about? You do realize the application we are talking about (G-Map) does NOT have voice prompting???
I have used the iPhone 3G with Google Maps and its GPS extensively, and it frightens me to think that people are using that while driving a car. Its dangerous. You state that you use Google Maps a lot and it does everything wonderfully. Have you used anything else to compare it to? I have to wonder.
I will explain again why Google Maps is dangerous if the driver is using it. First, you must continually hit the "Next" button at every turn (or segment of a turn... 3 times for some ramps). After you hit next, you have to reactivate the tracking. This requires putting way too much attention into watching exactly where you are on the Google Maps display... otherwise you can get off track entirely or loose track of which turn segment you are on. Which brings me to point two. If you do get off track by accident, or intentionally alter your route, you have to start over and re-type your destination. If you stop every time you do any of this, then you are being safe. If you don't, then you are not. Google Maps does require a lot of attention to navigate with.
Compare that to "turn by turn" instructions. You put in your destination. It gives you a route. It automatically prompts for the next turn after you make a turn. And if you get off the route, it automatically re-routes you. It has nothing to do with "3D maps" or "voice prompts" as you've said. The point of using navigation software, be it Google or G-Map, is that you don't already know how to get where you going. That means you are driving on unfamiliar roads and should be focussed on your driving. The point of "turn by turn" instructions is that you take the time to put in your destination BEFORE you start driving. After that, the navigation software doesn't require any more interaction to distract the driver. Can Google Maps get you there? Sure. Is it safe? I would say that its not unless you do a lot of stopping and going or have a navigator that is hitting the buttons for you. If you are so concerned with safety, then this should be a concern.
There are other devices out there to meet this "need" as you've called it. I have a Garmin Nuvi. It does a wonderful job. It was $250 which compared to $20 I wouldn't call "cheap" as you did. My wife uses the Garmin. I could have bought a second one, but why? I have a device in the iPhone that works pretty well with the proper software, and I don't have to carry a second device around with me. With the iPhone I can listen to my music, respond to phone calls, and do my navigation in the same device. This is what having a "converged device" means.
If you like Google Maps, then use it. You don't need to put down people who want a more capable application for navigation. There are good reasons for it that are based on convenience and safety. G-Map has proven that the iPhone can do the job. For some unknown reason, Apple is choosing to block this function from the iPhone which is really ridiculous.