Thats a really poor implementation of multitasking i think. There has to be a way -when closing an app- to decide if it goes in the background or closes completely. In earlier OS versions you could just hold the main button for a longer time and you could kill frozen apps for example, but if you do that now the speech dial function comes on, so thats not an option.
So i hope they find another easy way to do that.
I just find it curious that nobody at Apple saw that problem.
Your issue isn't with multitasking but with how your application's developer chose to implement it. I haven't spent any time reviewing the new multitasking functions but as a software developer in general I don't see any reason why your application couldn't be programmed to allow you to easily handle this situation. You shouldn't be blaming the platform, you should blame the application developer.
For example, Trapster uses the GPS and they recognized that some users like yourself might not have the forethought to realize that leaving a multitasked GPS application running will eventually wear out the battery. The Trapster developers added a method to notify you that you've left the GPS running so you can choose to close the app or not. Their solution wasn't eloquent in my opinion, but functional.
At this point you shouldn't find fault with how Apple chose to allow multitasking and instead provide adequate feedback to your application developer so they can enhance the application to work better for users like yourself.