I then coudl not play them in any other browser without installing QuickTime, is this expected behavior?
Yes, podPress does not include a player for mp4 files and requires a browser plugin like QuickTime which can play mp4 files. It does not has to be QuickTime. But if you can play mp4 files on a computer or mobile device it is likely that such a browser plugin is already installed. Sometimes you can select inside the browser preferences programs which can handle the different file types.
It is planned for the future to improve podPress and to add better support for mp4 files. But I can't tell you when this will happen.