You don't need to copy the pixels into the streaming texture's pixel data. This behavior is defined specifically to optimize the UpdateTexture path.

Xcode-iPhoneOS/Demos/src/happy.c

@@ -164,7 +164,7 @@ main(int argc, char *argv[])
         } else if (delay > MILLESECONDS_PER_FRAME) {
             delay = MILLESECONDS_PER_FRAME;
         }
-        //SDL_Delay(delay);
+        SDL_Delay(delay);
     }
 
     /* cleanup */