for a web page to display using the fonts you are setting, those fonts must be installed on the clients computer.
The fonts you are trying to use are not standard fonts that everyone will have available on their system.
If the css is trying to use a font that is not available on the clients system, the browser will default to one that is.
See the following article for a listing of fonts that are commonly installed on the client systems:
Is is possible to embed the fonts on your page, but in reality, embedded fonts are only supported in IE:
It is best to stick with the standard fonts that all users will have installed on their systems.