Is NAS / SAN + HTTP server a good solution for serving large number of static files over the internet?
Add some memory caching on your server, and you should be good. Apache has a couple of modules that do that.
You could also take a look at static distributed caching services, if you want to improve latency for your users and reduce your bw costs, like Akamai and PantherExpress. The latter can be a good investment, depending on your bw costs.