They're smarter then that, you actually do download the game, but they just forget to mention that. There's a cache located somewhere on your disc.
d = System.getProperty("user.home");
//a lot of other code
if(~j1 > -33 || ~j1 < -35)
j1 = 32;
String as[] = {
"c:/rscache/", "/rscache/", "c:/windows/", "c:/winnt/", "c:/", d, "/tmp/", ""
};
String as1[] = {
".jagex_cache_" + j1, ".file_store_" + j1
};