Wrong -- iOS apps can use more than 32mb of RAM. On the 128MB iPhones and iPod touches, there was only about 30MB (actually a little less) available. On the 3GS, the OS didn't take up much more space, so apps could now expand into about 150MB or so. iOS 4 introduced multitasking, but apps in the background can still be closed if the OS or the foreground application need more RAM. Therefore, there is still a lot of RAM available to apps , even under iOS 4.
On the iPhone 4, there should be even more RAM available. If this rumor is true (I have some doubts given the lack of RAM on the iPad and the 4x pixels of the retina display -- waiting to hear results from a developer first), then there won't be many apps released soon that will take advantage of the extra RAM, since only the iPhone 4 will be able to support it (for now). But as time goes on and the 256MB iOS devices are replaced with 512MB and higher, there will be apps that use that extra space.