Google has launched Latitude for iPhone and iPod touch in the form of web application and not as a native application. You can take a look at What is Google latitude for undestanding about this application. Now the reason why Google latitude is released in form of web application is that Apple requested so in order to avoid confusion with Maps on the iPhone, which uses Google to serve maps tiles, as mentioned by Mat Balez, Product Manager, Google Mobile Team at Official Google Mobile blog.
Latitude is supported for below mobile devices, says Google
More details on what is Google latitude can be found in my earlier post Google latitude.
Stay tuned for more.