Because your browser is incredibly carefully sandboxed, and your desktop is not. Worse yet, even the low level of sandboxing that desktops posses are almost al

Because your browser is incredibly carefully sandboxed, and your desktop is not. Worse yet, even the low level of sandboxing that desktops posses are almost always defeated by installers: "This installer requires administrator privileges to run" ... aka. yes, you will take our spyware-crapware-rubbish, and you'll love it, or you wont use our app. Capish? You don't get that with websites. That's why it's ok. (Incidentally, this is the same reason why its not ok on mobile platforms, where your options of permission are to read your contacts and make phone calls and 'services that cost money' or no, you can't play this game of Cat Pong your friends are talking about...)