You're contradicting yourself here. Many of them don't have fans either.
AppleTV has an internal CPU that generates a lot more heat than a standalone Firewire drive will. But for that matter, you can get external Firewire drives that are better ventilated and have more capacity for the buck.
If you stick a larger drive in the AppleTV, I guarantee you the markup is going to increase the price more than the cost of the same capacity standalone drive.
tv once I have a HD TV, but that will be a few years yet I suspect. By the time I have both, I would prefer to have 1080p as well as internet access, bigger hard drive and the option to plug in a tuner for recording. This last feature would be great if you could use it to record from an eyeTV and either watch later on