The problem with expect to developers to create a latest.php file is that not everyone will remember to update the version each time new software version is ready (except if they're using some automated versioning software like Trac).
Another good thing should be create a collaborative website like http://osx.iusethis.com/
for Mac apps, where the user (or developer) can add the latest version and download link, and using something to validate the information (a voting system Digg like?, or maybe a wiki correction system?) then the system will output all results (query based) in one file that can be accesed with your program and the download links directly (or page to go and download).
I can help in the website if you want.