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Well, with the 40 subscribers, assuming that they paid $30 for the year, anand already has enough $$ to run a T1 for two months 
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But the forums probably aren't utilizing just a T1. And then there are the hosting, monitoring, and security concerns. For a site this big it's a good idea to have 24/365 access to the co-lo room, and also on-site support for emergencies. Since the servers are hosted off-site, it's usually better to choose a secure data center than a smaller hosting company.
There are countless more services available. A single point-of-contact, on-site maintenance/management, Service-level agreements, etc... It's not uncommon for sites and applications not much larger than AT to cost as much as $30,000/mo. Assuming only 12-month subscriptions for $30.00, a site like that would need 12,000 subscribers just to offset the hosting/bandwidth costs.
It's no wonder so many online services have started subscription services
